I'd agree with what most have already said, but I'd also add that there is a feeling of 'chemical' if that even makes any sense.
When they inject you with the first solution, you can feel it working through your bloodstream I guess and even have a kind of 'chemically' taste in your mouth. Then you will feel like you are very drunk and like everything is kind of shrinking in around you. You start to want to close your eyes, then you just can't stop it and you are gone.
This all happens really quickly and it's not painful or anything to worry about.
The most bizarre experience I ever had with an operation was when I had my wrist put back together while I was living in Canada. As I went to sleep, the antithesist had asked me something and so I was telling him about it, when all of a sudden I was gone.
When I woke up, I was trying to continue the conversation, though he was no longer there! I then became really confused because the only voice I could hear was a British woman. As I came around, I realized the nurse was British and I then thought maybe I was back in the UK. It was only when I'd regained my senses that I was able to ask her!