I'm sorry to hear how you're suffering. I concur with Annuk, it's a good idea to go to the doctor. It might be a migraine, and if it is the doctor can give you something for the pain. As a migraine sufferer, my doctor has advised me to book an appointment whenever my headaches change so he can check there is nothing more serious occuring. Lasting five days is a change that would warrant a visit.
Just a note from your first message, tension headaches don't necessarily mean you're tense, they mean you're muscles are tight. Sometimes that occurs when I grind my teeth at night and I don't necessarily need to be tense.
It sounds like you're handling this well even though you're scared. Have you asked the doctor for a medication to stop the headache? I would think they could give you something to relax your muscles and make it go away for the time being.
Good luck. I'm thinking of you.
I'm glad to hear you visited the neurologist and he did some tests. Do you feel better that he is getting close to a diagnosis?
To quote my psychologist, "worrying doesn't accomplish anything". (I know that's not always helpful when you're worrying. ) Even though it's scary that he's doing a test for a growth and your reflexes are weaker on one side, it might also be nothing. If the neurologist does find something, he's trained to help you and will be able to successfully guide you to the proper treatment. There's a very good chance things will turn out for the best and you will be okay. If something serious is taking place you can deal with it then, rather than worry about it now when you don't really know what's wrong, what the possible treatments are, and the chances of success or failure.
I hope that perhaps I have put your mind at ease a little bit. If not, I'm sorry and I'm thinking of you. Try not to worry.