I had one last year and opted to stay awake for it, which in hindsight really wasn't the best decision for me. However the staff were truly amazing. Aside from the person actually doing the endoscopy, there was also 3 nurses in the room. One sprayed the sedative in my throat, and then when I started getting a bit panicky, she told me to press my fingers to my throat and feel myself swallow, which was hugely reassuring. At the same time, another nurse asked me what music I liked and then put some onto play. Then whilst they assisted during the endoscopy, the third nurse sat beside me literally stroking me hair and talking to me constantly. As Sabbie said there's a lot of belching which can feel strange but it's important to take deep breaths and stay calm.
Afterwards I went into a recovery room with everyone else, then after a quick check up I was allowed home. My throat felt a bit sore for a few days, but nothing major.