Recurrent and chronic pain, especially that originating in the lower back and/or neck, are common medical complaints for which the recommended treatments range from conservative (e.g., bed rest) to highly invasive (e.g., spinal surgery followed by bed rest).  Treatment recommendations vary because no single mode of therapy has been generally recognized as superior.  Each treatment choice is associated with its own costs and side effects, but recovery is typically prolonged, painful and expensive regardless of the choice.  See, e.g., U.S. Pat.  No.  5,653,665, which is incorporated herein by reference.  And the pain may be aggravated by poor sleeping habits (e.g., a tendency to sleep face-down).  See, e.g., U.S. Pat.  No.  6,073,288, which is incorporated herein by reference.  The resulting state of chronic pain predisposes patients to insomnia and excessive use of medication, thus increasing the cost of medical care and risking the development of dependency. 
Chronic pain that is actually precipitated or aggravated by bed rest is also often reported by patients confined to bed for reasons such as accidental injuries or cancer.  A common condition in all such periods of bed rest is that the patients are often not really at rest.  Rather, they are propped in a variety of positions that are moderately comfortable for only a limited time.  Movement out of these positions typically induces more pain.  See, e.g., U.S. Pat.  No.  6,807,698 B2, which is incorporated herein by reference (hereinafter the '698 patent). 
For some bed-ridden patients, movement is so restricted by the attendant pain that blood circulation and respiration are sufficiently compromised to lead to development of decubitus ulcers and/or pulmonary complications.  Attentive nursing care can alleviate such problems, but at relatively high cost.  Several therapeutic beds have been proposed to provide a minimal level of patient movement in the form of controlled oscillatory support.  See, e.g., the '698 patent as well as U.S. Pat.  Nos.  5,299,334, and 6,691,348 B2, and 6,708,358 B2 and 6,862,761 B2, which are incorporated herein by reference (hereinafter the '334 patent, the '348 patent, the '358 patent and the '761 patent respectively). 
To support an immobilized patient, the '334 patent discloses a generally rectangular patient support table that can be pivoted about transverse and longitudinal axes.  The '348 patent describes features alleviating the drawbacks and difficulties of prior art beds for a bed-ridden patient who is physically unable to move himself.  Both the '334 and the '348 patents describe structures to restrain or limit movement of a patient's body during tilting or tipping of a bed (i.e., preventing a patient from falling off the bed).  But neither '334 patent nor the '348 patent describe features designed to allow a patient to move by himself or herself so as to assume and/or adjust postures commonly observed in natural sleep (e.g., a lateral recumbent position with knees and hips flexed, a position known to relieve lower back pain).  See, e.g., U.S. Pat.  No.  4,910,818, which is incorporated herein by reference, and U.S. Pat.  No.  6,374,440 B1, which is incorporated herein by reference (hereinafter the '440 patent). 
A person lying in a right lateral recumbent position (i.e., with the person's weight being supported primarily by the person's right side), with knees and hips flexed to relieve lower back pain, is shown schematically in FIG.  1 of the '440 patent.  While this position is temporarily beneficial and may even induce sleep, the weight of the patient's uppermost arm, combined with muscle relaxation that accompanies sleep, tends to twist the patient's upper torso into a face-down position while the flexed knees and hips prevent the patient's lower body from turning with the upper torso.  The result is a twisting of the patient's spine which can aggravate lower back pain.