'Cold sleep' (a.k.a. 'hibernation' or 'hypersleep') is the name given to the artificial sleep in which passengers in Low Passage are put.
- They 'sleep' in a state of unconsciousness in special containers where they do not age (or very slowly).
- A "Low Berth" Cold Sleep Unit is a device that functions as Ship Equipment.
Putting someone in cold sleep and waking them back up is quite dangerous and the individual may not survive it. Certificates that the individual underwent a proper medical examination in the previous year to ensure they are healthy as well as a trained medic are required.
Non-canon: 'Low berth' are usually completely sealed containers with a window to observe the 'patient' from the outside (more for psychological reasons than out of technical necessity).
- The technical features vary according to the TL.
At low TL, the technologically is crude and requires the patient to wear a special suit, with many tubes connecting it to the container itself for the many sensors, but also for the various body fluids the container and the patient will exchange, including several catheters and probes. In particular, the blood of the patient is mixed in high ratio, or sometimes even completely replaced, with an artificial fluid whose function is similar to formaldehyde : preserving the body from decay. Other fluids which need to be controlled include oxygen (or other breathing gases), saline solution (to control body dehydration), excrements and so on.
- At the end of the cold sleep, the artificial preserving fluid is filtered out. No need to say, this is somehow traumatising for the body, which explains why cold sleep is risky for the health of the patient.
- The normal procedure to put somebody in cold sleep or waking him is progressive and takes some time (from several hours up to a day). It is possible to wake up someone more hastily, but the risks for the health of the patient are much higher and only used in life threatening emergency situations.
- Gravity control technology is also used to avoid that the body rest always in contact with the container on the same parts which could cause oedema or tissue necrosis. For low berth of lower TL where this technology is not available, the body is usually immersed inside a fluid of the same density as the body (i.e. same as water) which keeps the body floating 'in between'. According to the available TL (and patient's organism), a breathing apparatus may be necessary or the fluid may be directly breathable ().
- At the other extreme, at much higher TL, the patient just lays down on a comfortable couch and sleeps and wakes up just like they had had a nap.