I'm not sure I'm going to be able to get myself to do it. I would never consider it if I had other options.
I don't think it's doable. I'm not an expert and don't have first hand experience but I think first it would take hours of exhausting yourself, then you'd reach a point of panic and confusion which could last half an hour, where you might start backtracking trying to save yourself, then if you haven't managed to, comes the point when you are almost out of energy and you keep breathing in splashes of water. Finally you have no more energy and drown, experiencing awful awful asphyxiation.
But the above is optimistic. If you're fit and healthy the above could even be drawn out for a day and a night of exhausting yourself before you finally drown.
I know you say it's your last option but it's not a good way to go, involves a lot of suffering, and will test your willpower and SI to its max. Chances are you'll reach a point where you just want to get out of the water and crawl back into bed