Talk:Frostbite/@comment-86.115.4.151-20200404080418/@comment-108.252.224.231-20200411210841
It's possibly you had an exposed bodypart, such as a Hands or Feet, or if you slept for a long period of time (e.g. 8 hours all at once) that the weather dropped below freezing, you got the frostbite, and then went above freezing and healed the Hypothermia risk before waking up.
This happens more commonly on higher difficulties (Stalker and Interloper) especially if one tries to sleep in a potentially cold place for many hours at a time.