Welcome to HCM
We understand your concerns
I went through your description of the problem and I feel the experience your friend had was due to tiredness
or over exaustion.
When we are over exausted, our body is so tired, it just needs rest and proper rest, nothing short will be accepted. Such a sleep should be totally unaware of whatever happens around. Sweat must have happened due to climatic change or using of a blanket unknowingly. Sweat broke his sleep suddenly and he felt panic triggering palpitation
and further sweat. Then calming down took place and he felt cold
due to the sweat present. Hopefully that is the clear explanation.
Therefore nothing to worry. May be, if you want to be doubly sure, do visit a general physician.
Hope I could clarify your doubts. Available for further clarifications.