Psychill is a form of electronic music that is characterized by low tempo, relaxing rhythm and melodies, and a large variation in use of percussions (compared to other forms of electronic music, especially EDM). Psychill is used for the purpose in the name, chilling out, or relaxing. It has been found by this noder and a few others that Psychill can have strange, semi-intoxicating effects if listened to for extended periods, usually around an hour, although YMMV. These effects can be described as a sort of high similar to those induced by illegal substances like marijuana, although this is coming from someone who has never partaken of that substance.
A simple theory regarding how these effects are induced regards how sound affects the conscious mind, relaxing it and, in some cases, controlling or guiding it. There are forms of music regarded as the "most relaxing" which gained their title through use of sound which lowers heart rate and calms the mind. Psychill is known for having these effects as well. For those interested in Psychill, I would personally not recommend singular songs, as they are too short to give the full effect. Rather, I would recommend "mixes", series of songs edited together in such a way that there isn't a clear division between songs, allowing the listener to extend listening time with less interruption. Mixes of an hour in length or more maximize the effects previously mentioned and can be used for multiple purposes, such as general relaxation, gentle ambient music for background play, and music to listen to whilst performing otherwise monotonous activity like surfing the internet or writing.
For a good mixer, I would recommend Spacemind, who can be found on both YouTube and Mixcrate. Additionally, his mixes are available for free download on Mixcrate.
Related forms of music include general Ambient and various forms of Goa.