Things I Learnt The Hard Way - When It's Time to Stop, It's Time To Stop

Learn when you can't code anymore.

Learn when you can't process things anymore.

Don't push beyond that, it will just make things worse in the future.

I tried to keep coding once when I had a migraine (not strong, but not mild). Next day, when I was better, I had to rewrite most of the stuff I did, 'cause it was all shit.

Also, when you're not feeling fine, you won't be able to concentrate and your productivity will plunge. It's a lot better to be a burden to society at your own place than a burden to society at work.