I'm riding the same ride. I have had most of the same complaints, especially the head pressure and nausea. I forget if you are on meds right now....will check out your page. Hang in there, there are good days too.
Maybe I stole your thunder? I started the day feeling heavily fatigued and awful. It hurt my hand to even hold a pen, both arthritic pain in the bones and nerve pain in the skin. I thought I was doomed to go home early on sick leave...
Then mid-day I started to rally and ended up working a total of 12 hours today! OK, I cheated and had an afternoon mocha that surely helped. I know I'll crash hard and need to back down tomorrow, but I completed an important work task that had been hanging over my head for far too long, so I'm pleased.
You're not the only one on the ride. I've had days where I think I'm doing well, only to have it suddenly reverse. Just keep in mind it can work the other way, and hopefully eventually it'll all even out at a position of good health.