So we’re not really sure what happened.
Going to the sloped aft ramp with not much to hold on to, with nausea and no tether, sure seems dangerous enough to just slide and fall out of the aircraft. But this still seems to conflict with the little evidence there is: the SIC was “upset” and “apologized”, none of which are a clear sign of nausea (although he did open his side window). If the ramp is open, I presume you would already get plenty of fresh air before reaching the sloped ramp itself.
There may not be as much to learn from this, but I definitely see the loss of judgement as a potential cause, in which case following standard procedures can help. Also having ways to identify (partial) loss of judgement / degraded cognitive performance and act accordingly (search for situations well within experience limits, etc.).
