Cryostasis: Sleep of Reason (Ukrainian: ???????: ??? ??????) is a 2008 psychological horror video game developed by Action Forms for Microsoft Windows. The game story develops with help of a unique system called Mental Echo – the ability to penetrate another character's memory and change the actions taken by that character in the past. This can involve saving people's lives by taking over their bodies in their memories and changing the course of history. The game being set in an arctic setting employs body heat as a health meter – the player must use heat sources (such as lights or stoves) to replenish health. The gameplay is from a first person perspective.