Brain tumor removed 4 years ago. have been having partial/complex seizures, but two days ago i've had my first grand mal seizure. why now?

Could be: residual scarring, unrelated condition that lowered your seizure threshold, or even recurrent tumor. Consult again with your neurosurgeon.

Brain tumor: There are a variety of reasons that you could have suffered a grand mal seizure. First, an MRI of the brain is necessary to exclude a recurrent brain tumor. Second, an EEG may be needed to identify the location of the seizure. Third, missing a medication dose, lack of sleep or food, stress, infection, or other medical problem can trigger a seizure. See your neurologist.