Appreciate the cautionary input Coja. Never can err too far on the side of safety.
Of course brother Benz is correct in saying that basically all Dissos can have negative side effects... particularly if you abuse them. Personally, the idea of doing DXM even 2 days in a row seems crazy, but there are walking cautionary tales around who managed to take the stuff like it was vitamins... and paid the price for it.
The fact that people who seriously abuse a substance can be found with lasting negative effects does not indicate that a substance can not be used safely by people with a bit of intelligence and self control. People who get addicted to DXM and regularly 4th plateau for days on end, for years can not be too surprised if they have some cognitive issues. I think the equivalent of that in classical psychs would be like taking a 10 strip of acid 5x a week for a few years. (you can find some fools with stammers, inability to cope or full on residency in a nuthouse who followed that diet)
I guess you could mess yourself up pretty badly if you abused Fatburgers and milkshakes.
I don't think anyone needs to Dex more than 2x a month and even that might be overdoing it. Furthermore, no one really needs to ever take more than 7.5mg per kg. Say 8 to be sure if you are a hardhead. 4th plateau is NOT better than 3rd. (and Sigma is just stupid)
Most important IMHO is drinking tons of water. And the need for darkness.
As for the tub issue... DM Turner got electrocuted taking a bath during a thunderstorm as far as I know. A slightly different situation.
I think a sitter is a good idea anyway, but if your tub is not so big that you can easily slip underwater, you should be fine. (i.e. If your feet touch the far end) IMHO DXM is not meant to knock you out or have experiences where you have no connection to your body. At the ideal dose, you can travel the cosmos without losing contact with your body. K-Holing is not really equivalent to upper plateau DXM in this. I can not speak for others (we're all different), but back when I was taking DXM there was very little chance I could drown on it... short of someone knocking me over the head with a 2x4.
At any rate, be safe. Do not take anything on this thread as any kind of encouragement to use DXM... and certainly not to abuse it.
Take care.
HSF
"Curiouser and curiouser..." ~ Alice
"Do not believe in anything simply because you have heard it. Do not believe in anything simply because it is spoken and rumored by many. Do not believe in anything simply because it is found written in your religious books. Do not believe in anything merely on the authority of your teachers and elders. Do not believe in traditions because they have been handed down for many generations. But after observation and analysis, when you find that anything agrees with reason and is conducive to the good and benefit of one and all, then accept it and live up to it." ~ Buddha