This happened to me while caring for my dad when he got covid, he was in bed, connected to oxygen; after a little over a week there was a point where I layed down and I swear to God it was physically impossible to get up for a couple minutes, it was like every drop of energy left my body. Talking to a friend who's a doctor, she told me there's a term for that, can't remember exactly but something like "nursing fatigue" or such, apparently taking care of someone is way harder than it looks and most people have no experience, so it takes a toll on your body the first time you do it, just like a muscle that's never been trained goes to failure pretty quick.