It varies between people. The scan itself cannot be felt, and you simply lie on the table in a given position and follow instruction where relevant. I scan babies while they sleep on a regular basis, and most times they sleep right through the procedure. The positions we use for wrists and elbows can be quite awkward, but a brain scan is very simple and straight forward unless you have breathing difficulties.
The only thing that could be uncomfortable is if you are given IV contrast. Effects vary widely, as seen in prior responses, but typical effects can include feeling a warm flush throughout the body, feeling like you’ve wet yourself, and a metallic taste in the mouth. Be sure to answer the allergen questionnaire accurately, as it is possible (but very rare) to have a severe anaphylactic reaction.
However I wonder if a CT scan is in fact the most appropriate test for your symptoms. CTs are often requested before an MRI due to economic considerations, but MRIs are the gold standard for neurological imaging. The main things CTs are better for in terms of brain scans are bone-involving lesions, acute medical emergencies such as stroke and bleeds, or calcification. I would consider talking to the radiologist before you have your scan, and asking if MRI isn’t a more appropriate test for your symptoms.