Try not to worry. I know, easier said than done! I had a colonoscopy last year and felt nothing. The prep was unpleasant and I would recommend Sudocream as the constant wiping left it really sore. But I felt nothing during the procedure. Yes, you hear of people having awful experiences but those are the ones people are likely to talk about. 

Hello there and thanks for posting

I am sorry to hear you are undergoing tests following a positive FIT test and appreciate how worried you are about having these done.

Try not to over think this if you can, at your young age there is likely to be another cause for the positive fit other than cancer. Blood in the stools can be the result of infection, haemorrhoids, and many other inflammatory bowel conditions including ibs, crohn's or ulcerative colitis so try not to let your mind run away with you.

I think it is important to talk through your fears with the team involved so they can reassure and make sure things are put into place to help you through so do telephone them ahead to discuss this with them.

General anesthesia isn't usually offered and I don't think you'll be able to ask for a GA either as sedation is usually adequate in most circumstances. 

Wishing you all the best

Take care

Naomi