My strongest medical advice is this: tell your doctor what you are worried about. Here’s the thing- if you are scared that your headache is a brain tumor, and don’t say that to your doctor, there is a very good chance that he/she won’t specifically say "you don’t have a brain tumor" and you probably won’t leave feeling any better.
Believe me, doctors aren’t mind readers. A lot of people don’t say what they are really worried about because they are scared to hear the diagnosis, or they are worried that the doctor will think they are crazy or blow them off. For the most part this isn’t true. For one thing, no matter how crazy you think you are, you just aren’t. I’ve heard a million people more crazy than you. For another, a good doctor will not ignore your concerns regardless. And here’s the most important point- you either don’t have a brain tumor, and will feel better after be evaluated for it or (less likely, but possible), you have a brain tumor and you need it diagnosed and treated as soon as possible.
I know a person who started feeling dizzy. She was dizzy for about a week, but didn’t tell anyone because she was worried that people would think she was crazy. She then realized that she was actually dizzy because she had lost a good portion of the vision in her right eye, and so had lost depth perception. She then self-diagnosed her scotoma as multiple sclerosis. She still didn’t tell anyone, or go to the doctor, because she was terrified of being diagnosed with such a devastating disease. She never saw a doctor until she mentioned her recent sudden blindness to her husband who freaked out and told her not to come home until she saw an ophthalmologist. Within fourteen hours of finally seeing a physician she was being prepped for surgery to repair a detached retina.
If you’ve been around here for a while, you probably know this particular dumbass was me. My fear and stubbornness cost me two eye surgeries and the majority of vision in my right eye. If I had gone to the doctor right away, the chance of success of the surgery would have been much, much better.
So, there it is. If something isn’t right, go to the doctor, and actually tell them what is scaring you and why. Say "my mother was just diagnosed with breast cancer and I’m worried that these twinges in my chest are cancer too" rather than "I don’t feel good" and you won’t leave the office still scared. And if you find a lump go to the doctor as soon as you can, because ignoring it doesn’t make it go away. It just makes it worse.
Do me a favor, and do as I say, and not as I did.