For my new year's resolution I joined the gym. About a week ago, I went to the gym for the first time in years. I ran about 3km on a treadmill and then about a kilometre on a cross trainer. After that I did some sets with dumbbells and that was it. I was pretty exhausted, my HR was high the whole time and I was nauseous from the exercise - I went pretty hard. After I walked home(it was pretty cold and I went without a cap or a scarf) I made dinner and suddenly I developed a headache. I never get headaches except when I'm hungover or I have a fever. The headache lasted for a few hours, so I decided to go to sleep. After I woke up, the headache was gone. It didn't bother me at first, but today an intrusive thought popped in, you know, the usual "what if". Now I'm worrying about a brain tumor, because I've read that there is a thing called secondary exertional headaches, which occur after a workout and may be caused by a brain tumor or other problems. I don't really have any other problems which I'd attribute to a brain tumor, but this thing haunts me since a few years :(