What exactly causes headaches when you're coughing & coughing quite often and quite hard?

I've asthma and at the moment think I might have a chest infection or something, lots of phlegm, blocked nose, sometimes hard to breathe even after taking asthma inhalers. Sweating like a pig and every time I cough get a severe headache - almost like my brain is bumping up against my skull, lol. I know that's not what happens of course but what does actually cause a headache when you cough like that? Blood vessels or something? Thanks.