mouse1~
I too am in the same boat with regards to exercising and getting screaming headaches. I can walk and have been able to but it's terribly hard to shift gears mentally and physically from a dedicated swim, bike, run lifestyle to one of only walking.
Swimming laps even at 50 yd intervals will generate a "exercise induced migraine" as my neurologist calls them. They suck. Cycling will cause them to last for 5 days, and will resort to my stock of Naratriptan, which will take the pain away but it still leaves me off-kilter cognitive wise.
I'm meeting with a physiatrist this next week with my cervical MRI films, maybe he can see something which may have been overlooked initially.
If you can walk, indeed try to keep that up regardless of pace, it will keep the brain fresh with oxygen.
Mike