Try Bikram yoga. For first-timers I think they offer a week of unlimited access for twenty dollars US - a fairly low-cost test. It's quite physically taxing - in the 90 minutes of the session, for perhaps only ten interspersed minutes, if that, does the sympathetic nervous system even have a chance to give way to the parasympathetic. I assume that those times would be the most risky for you, and of course cannot speak to your experience, but I find it difficult to imagine your imagined stress will be sufficient enough to convince your sympathetic nervous system to activate during those times; it will be quite exhausted already.