The day that you describe was packed with activities. Your kids sound like mine, the more you give, the more they want. When their father is taking care of them, he'll sometimes clean the entire house from top to bottom at the same time!! Makes me look a right fool when I complain I don't have time to vacuum when I'm with DCs!
But, they demand more of me because I give more. I know this. It's all screens and grandparent visits with DH. He doesn't play with them at all.
Like you, I have a chronic condition and could easily fall asleep on a washing line come 4pm.
My advice is TV afternoons, where you sit and watch TV too!
When they're home from school, snack them up, give them a screen each and sneak upstairs for as long as they'll let you and drink a cup of tea in peace before you battle dinner time. I hate meal times. My DCs talk at me full pelt throughout and I feel exhausted by the end.
At the weekends, take a couple of hours/half a day to yourself of possible. Lock the bathroom door and just lie in the bath.
Be authentic with your kids. Tell them how knackered you are, tell them how demanding they are, tell them if they're being ungrateful and expecting too much of you.
I've had 3 burnouts in 7 years. I had hives, ached all over, migraines, diarrhoea. Diagnosed with chronic stress both times. Don't do that to yourself.
Take a bed or bath day now and then.
Sneak off for a masage or facial.
I can't do a thing during week day eveings as I'm knackered... so weekends are your friend. Get childcare and do something for you, especially if that means doing nothing.