Christ, the seizure alone must be a worry. And you'll be so tired and wobbly anyway from all that.
Most brain tumours are benign and are removable but the surgeon will check they don't start growing back every year or so. Medicine's a lot farther along than we think about brain tumours.
I am trying to say don't be petrified but you must be so drained and shocked that's probably a really annoying thing to hear - so stick to the basics. Have you had supper. Eat as much as humanly possible.
Do deep breathing to calm yourself down, works altho it's boring and I prefer a fag. Drink tea and gin alternately. Matt & Socks won't care if you're pissed, they might get an extra meal out of you.
The likelihood is that the waiting is the very worst bit of all. You are not alone tho.