Well if you're going to kill yourself, slow hypoxia is the way to go. Apparently you can feel quite relaxed. There was an incident with an airliner here in Ireland a few years ago. It failed to pressurise for some reason. The pilots didn't notice because they were becoming hypoxic. Only the repeated intervention of one of the cabin crew and finally the deployment of the passenger oxygen masks convinced the hypoxic Captain to descend. He later had very little memory of the events.
The problem isn't so much a fast depressurisation which will be pretty obvious. But a slow insidious depressurisation. That's the dangerous one.
