Nervous about laughing gas

I’m going to the dentist next week, the dentist said I need a fill in on a particular tooth that we are going to take care of, he gave me a choice between laughing gas and local anesthetic. (Numbing just half of my mouth with a shot). I naturally have low bp, and normally In the past when I have had the local anesthetic it lowers my bp even more and I feel faint. This is why I want to ask for the gas because I want to avoid that, but I’m very nervous because I’ve never been completely put to sleep for anything before. Does anyone have any experience with it they would like to share to help a girl out?