In a first, an American woman used a suicide pod to take her own life. The process took place in Switzerland. It’s done by pumping in only nitrogen gas, so the person will lose goes dizzy, loses consciousness and eventually dies. Enter futurama memes.
The speed can significantly vary with CO2. I don’t like it much myself, but due to how hemoglobin works it forces your lungs to work backwards and dump oxygen like you were in the vacuum of space. Unconsciousness is generally very rapid compared to other asphyxiants.