Hello, Welcome to Just Answer and thanks for your question. No one can give a diagnosis of anything without an examination and the tests that are required based on the examination and patient history. Dizziness and lightheadedness can be from many things from food allergies to ear infections with lots of other possibilities in between. A brain tumor would not be anywhere near the top of the list. Since you are being freaked out by this unlikely cause, that makes anxiety disorder one of the possible diagnoses, but you will need to see your medical practitioner to determine what it is.
I'm sorry you don't understand but that has nothing to do with the answer quality.
Perhaps I can make it a little simpler for you.
Dizziness and lightheadedness can come from:
There is no way to tell what is wrong with you without seeing a medical practitioner in person. It is impossible to diagnose anything online.