Hypoxia involves inadequate levels of oxygen. Unlike asphyxiant gases (e.g. nitrogen or CO2) which achieve their effect by lowering blood oxygen levels, nitrous oxide has an anesthetic effect even when oxygen is present in adequate amounts.
I think of a buzz as being a steady state. What I’m talking about is a specific event. It’s like a vibration going on in your mind and body over a few seconds, and speeding up, like a coin spinning down to flat. They are all the same kind of experience to me, but I stopped even thinking about using nitrous decades ago. It’s a rush, but I’m curious if it has a medical definition.