I'm just the same. Was the course all day? I find I need some "chill out" time after a few hours.
Here's my day so far:
woken by alarm at 7.45am. Struggled to get up. Bathed and washed hair. Drove 15 miles, mainly motorway, to friend's house. Had a cuppa, walked dog there for almost 5km, stopped for more tea and cake, drove back home via petrol station and local shopping centre where I bought a couple of items. Got home about 12.30pmand neighbour wanted to talk about his fence. Invited him round to look at fence. Hung out washing. I am now really tired and would like to go and lie down. I've not yet got to the absolutely HAVE to lie down stage yet though. I've got a doctor's appt late afternoon, after which I should go to Yoga for 7pm. Not sure I will last that long though so may in fact miss Yoga.
Like you, I couldn't contemplate full time work after I had the kids and now live alone but still couldn't manage more hours.
I feel really feeble when I read what others manage to do. I do have an underactive thyroid but I've been on meds for that for over 20 years now.
My elderly neighbour and his ladyfriend, by contrast, seem to manage to cram a heck of a lot more into their day.