I'm afraid i have a brain tumor. could dizziness and nausea from a brain tumor get better or ease up over time (one week) or would they get worse?

Brain Tumor?: Dizziness & nausea are very non-specific symptoms. While they may be a sign of a brain tumor, they may also follow a concussion, many viral illnesses, middle ear/sinus infections, and a whole panoply of other things. Did you suffer a head injury? Do you have any other symptoms, like a fever, pain in the sinuses, headache, or blurred vision? Consult your doctor if it doesn't clear up in a few days.

Can fluctuate: The nausea and other symptoms which some brain tumors cause can come and go, so your question is apt. It might be a brain tumor.And over time if it is this will get worse. See your doctor about this and ask for a neurology consult.