I'm going to be having a CT scan on my brain in a few days and was wondering what it involved?

Holding still 30 sec. Not much. Lying still on a ct table for 30 sec while a 3d xray of your head is generated with a rotating xray camera.
CT. The exam is very rapid, less than a minute, with limited radiation and high diagnostic yield. The machine is doughnut shaped and does not usually bother people who are claustrophobic.
Not much. A simple ct of the brain will require you to be placed on a sliding table called a gantry. This will take you slowly through the machine at a rate to take the pictures of your brain. You should not have any pain or discomfort. The scanner is usually narrow enough that you should not get claustrophobic. Should you require contrast with your ct, you will have an IV and the medication injected.