I also had a rough ride yesterday, after 4 forced days off (bike in the shop - it's finally back, was the bottom bracket. you were all correct). I was only able to go 6 miles, even though I'd planned on repeating the 12 mile route. I was riding 1-2 gears lower than normal, and after every hill, even little ones, I had to stop - felt like I was going to puke. After 3 miles, started feeling headachy, so decided to turn back. Got home and just sat on the floor feeling sick for about 20 minutes, but was OK after a cool shower and food.
I don't know if it was the time off that did it, or a change in diet (I also dropped calories 500 lower, about 5 days ago). I think I was hydrated - was sweating profusely and drinking a lot.
I'd like to figure it out too.