Sixty-five participants (14 men, 51 women) from three different companies with a mean age of 47.95 years (SD = 9.47) were included in the study. The participants were randomly assigned to a flotation-REST group (37 persons) or a wait-list control group (28 persons). Their mean number of monthly consumption of cigarettes was 47.23 (SD = 139.75), mean monthly consumption of alcohol was 172.90 millilitres (SD = 203.33) and mean number of used snuffboxes was 0.77 (SD = 2.87) every month. There were no significant differences regarding gender, age, cigarettes, snuff or alcohol between the two groups (independent samples t-tests, ps >0.256). The participants were all part of a cooperative-health project initiated by their individual companies. There was a wide range of occupational groups varying from managers, employers and employees all in the retail industry. The three companies had no part in any of the practical details regarding data collection, interpretation of results, study design etc.
A two-way split-plot design was carried out, where Time with assessments before and after the treatment sessions constituted the within-subject factor. Group (control group and flotation-REST group) constituted the between-subject factors. The participants were treated with flotation-REST during a 7-week period with a total of 12 flotation-REST sessions (45 min each). Several measurements (depression, anxiety, stress, energy, sleep quality, pain, optimism) were assessed before and after the treatment period. For the control group the same measurements were assessed before and after a 7-week period. After the period the control group also received flotation-REST treatment.
This study is registered as a clinical trial in Australian New Zealand Clinical Trials Registry (ANZCTR), as ACTRN12613000483752, and ethical approved by Karlstad University Ethical Review Board, dnr C2013/88.
SE - Stress and energy
This is a self-estimation instrument regarding an individual’s energy and stress experiences . It is based on two subscales that indicate the mood levels regarding: 'experienced stress' and ‘experienced energy’. The subjects are to answer certain statements that are placed on a six-grade scales, from 0 = not at all, to 5 = very much. Examples of the statements are “How much do you feel relaxed”, “How much do you feel tense”. The SE-scale is based on an early checklist, the Mood Adjective Check-List  and has been further modified and translated into Swedish . The instrument has been validated in a number of studies i.e. [21, 23]. Cronbach's alpha was 0.84 for the stress subscale, and 0.74 for the energy subscale. The score range is from 0 – 5 for each subscale.
HADS - Hospital anxiety depression scale
The HADS is a rating scale regarding degree of anxiety and depression. It was constructed for use with physically ill people , and has been validated and reliability tested . The HAD scale consists of fourteen statements with four response alternatives ranging from 0 to 3. Examples of the questions are ““Do you feel tense or wound up?”, “Do you take as much interest in things as you used to?” There are seven statements concerning anxiety and seven for depression, wherein values under 6 are considered normal, those between 6 and 1 are borderline, and all values over 8 points are indicative of a probable depression or anxiety diagnosis . The score range is from 0 – 21 for each subscale. Cronbach's alpha was 0.74 for the depression subscale, and 0.82 for the anxiety subscale.
LOT - Life orientation test
The test  consists of eight items plus four filler items. The task of each participant is to decide whether or not one agrees with each of the items described. The scale ranges from 0 – 4 where 0 indicates “strongly disagree” and 4 indicates “strongly agree”; the total score range is 0 – 32. The test measures dispositional optimism, defined in terms of generalized outcome expectancies. Parallel Test Reliability is reported to 0.76 and Internal Consistency to 0.76  and Test-Retest reliability to 0.75 . LOT is also regarded as having an adequate level of convergent and discriminant validity  as demonstrated by correlation statistics and by using LISREL VI (r = 0.64).
SQ - Sleep quality
This instrument consists of 11 questions that elucidate the sleeping habits . Responses to 9 questions are placed on a 0–4 scale, response to one question is placed on a 0–5 scale, and response to one further question is placed on a 0–8 scale. Examples of the questions are “How often do you feel tired on week days?”, “How often do you feel you did not get enough sleep?”, “How do you feel you usually sleep?”. The psychometric properties were examined by comparing healthy and sick people, and using Cronbach’s alpha (alpha = 0.88) . Score range is 0 – 45, and Cronbach’s alpha was 0.64.
Mindful Attention Awareness Scale is designed to assess the main characteristic of dispositional mindfulness . It measures whether a person is open or receptive to what is happening in the present and has a mindful state over time through a 15-item scale . The instrument consists of 15 items, all of which indicate a lack of mindfulness. The items are rated on a 6-point Likert scale ranging from 1 (almost always) to 6 (almost never). If the scores are rated high – it indicates more mindfulness of the subject (the total score can range from 15 to 90) . Cronbach’s alpha was 0.80.
Normal pain and worst pain
Visual Analog Scale (VAS). These scales were used for measuring normal pain and experienced worst pain. They consisted of a 100 mm horizontal line with the anchors “no pain” on the left extreme and “excruciating pain” on the right extreme. VAS is considered the “gold standard” for assessment of clinical pain, and changes in VAS score are regarded as significant evidence of individual response to treatment, placebo, or experimental manipulation . The accuracy and precision have been examined for both clinical and experimental pain, and found adequate .
EDN - Experienced deviation from normal state
This is an instrument that is constructed to be used in flotation-REST experiments based on the APZ-questionnaire and OAVAV  so that an assessment of altered states of consciousness and the relaxation response can be made. The EDN consists of 29 questions and these statements should each be responded to on a VAS-scale 0–100 mm (where 0 means “No, not more than usually” and 100 means “Yes, much more than usually”). Points obtained from these statements, are averaged so that an “index of experience” (0 – 100) can be measured . Through this, the total experience of deviation from normal states can be obtained. Examples of statements are “It seemed to me that my environment and I were one” and “I experienced past, present and future as an oneness”.
In earlier studies e.g. [11, 35] the EDN scale has been used where Cronbach’s alpha measured between 0.91 – 0.97, which suggests very high reliability for this scale; in the present study Cronbach’s alpha was 0.93. The average EDN-value following a person’s first encounter with flotation-REST is approximately around 30. Resting on a bed in a dark quiet room generates approximately 15 points .
Outer measurements are 2600 × 1650 × 1330 mm. In total it contains 600 litres of water and 350 kg’s of magnesium sulphate salt. To maintain a correct water temperature (approximately outer skin temperature, 35°C), heating foil is placed in the lower section of the floating tank, regulated by a thermostat and heated in regular intervals. The door is outwardly opened. The inside of the lower section had ribbed bottom to prevent slipperiness. Between flotation sessions, water is filtered and sterilized with UV-light along with weekly addition of hydrogen peroxide where oxidization occurs. The sterilization of water between flotation sessions takes approximately fifteen minutes. Filters are regularly changed and the inside of the flotation tank is cleaned twice a week in accordance to public health board recommendations.
An agreement was made between the owner of a flotation centre and three managers from three different companies about a health-care program involving flotation-tank treatments. All three companies advertised through intranet correspondence, their company magazines, and through emails, offering all employees to participate in the health-care program. All interested participants were invited to an information meeting at the flotation centre located in Deje in the county of Varmland, Sweden, where they were further informed about the program. Information was given that the flotation-rest program would enable them to participate in a scientific study concerning the effects of this treatment program. Further information was given regarding that the participation was voluntary, confidential, that they would be randomly selected to either experimental group or waiting list, and that they could terminate their participation at any given point. All participants made a verbal informed consent about participating. They were also informed it was possible to participate in the health-care program without participation in the present study. All participants filled out a questionnaire regarding basic facts (age, gender, alcohol consumption, nicotine use) as well as SE, HADS, LOT, VAS and SQ questionnaires. Data was collected by the manager of the flotation center.
After the introduction and data collection, the enrolled individuals were randomly assigned to either the control group or to the flotation-REST group (a total of 12 flotation sessions). Those individuals that had been randomized to the wait-list control group got the opportunity to later participate in flotation-treatments after the present study was terminated.
All participants were guided through the flotation centre. Participants in the flotation-REST group booked the 12 awaiting flotation sessions (around two per week for a period of seven weeks) where each session was of 45 minutes duration and 30 minutes to shower and relax afterwards. After the third flotation session a supplementary EDN questionnaire was filled out by the experiment group. After the last flotation-REST session, the questionnaires (i.e., SE, HADS, LOT, VAS, EDN and SQ) were once again answered by the flotation-REST group along with a complementary MAAS questionnaire. All questionnaires were filled out in privacy in a separate room (no staff there) and the participant put their questionnaires in a closed box, that were later transported un-opened to the researchers.
The control group was scheduled to return 7 weeks later for filling in the scales SE, HADS, LOT, PAI, and SQ again. All persons were treated in accordance with the Declaration of Helsinki, Ethical Principles for Medical Research Involving Human Subjects. Time estimated between first announcement of health project and completion was about 6 months. The participants suffered from no sick absence and were hence referred to as being relatively healthy.