I've got up to running outdoors for 25 minutes but have to stop (reluctantly) I find that each time I run, i end up with a very bad headache that sometimes last for two days. As per your suggestions, have tried rehydrating, eating bananas and etc but nothing seems to have worked. If I run in the evening- I seem to get a headache in the night and then am laid up for the next day. If I run in the morning, then by afternoon I have a dreadful headache.
I think it may be because i scrunch my shoulders while running and now have a stiff shoulder and neck. Going to give it a rest for a week or two and then start again taking it slowly if the headaches stop for the week.
It is very frustrating but I can't think of anything else that might help. The headaches have started once i began to run for 10 at a stretch.
Having 'googled' this i find the headaches seem to be a recognised side effect of running and exercising. Maybe its my brain coping strategy to this new fitness regime. I will keep you posted re the status of my headaches but signing off running for the next week or two.