Honestly, that kinda happened to me.
Well, I had a blood test because I was having heart palpitations and under extreme stress, so not exactly “just collapsed”. But they found I have hypothyroidism, and life’s much better and much easier with the medication.
Turns out you’re not supposed to feel tired after doing nothing, sleep 12 hours, then wake up tired…
Annoyingly this must’ve been an issue for years, but I was raised to “shut up and get on with it”, and told the problem was that I’m “just lazy” :/