Get Tylenol suppositories and caffeine suppositories. It will, at least, help you feel human and basically functional. You can also try kalei tzom (I think that’s what they’re called). They’re nutritional supplements (pills) that are sold at kosher supermarkets, and they’re supposed to help with fasting. I find that it does help a bit.
It’s also easier to fast when you haven’t been gorging all week (your stomach shrinks).