Tom:
And using that approach, a FFM could mitigate some of that risk, further changing the equation. Jim Lapenta pointed out that while a FFM might reduce immediate drowning risk, it's harder to gauge whether disrupted breathing might put the diver at risk for over-expansion injury on ascent (assuming that an epileptic might close their airway so gas couldn't flow out as it expanded). But at least part of the risk would be reduced.
I would like to know what type of seizure was had, at approximately what age, whether there were any known precipitating conditions (e.g.: fever, infection, medication or drug exposure, recent head injury), etc...
If the OP takes an interest in FFM's, be mindful they are a bit more complicated to work with. My wife has an old AGA Interspiro, and a buddy of mine has also used it. From their experience & observation with that specific model:
1.) It's strapped thoroughly on the head. Getting it off could be a bit involved.
2.) You can't donate an octopus readily to my wife unless she takes it off.
3.) At the surface, there's a knob/valve/what'cha'ma'call'it she turns to let her breathe ambient air, yet must turn off to submerge. You could take an unconscious person to the surface, forget to open it, and have them run out of gas & suffocate.
4.) It doesn't fog.
5.) It generally doesn't require purging.
6.) It's a bit harder to equalize; there's a plate of some sort pushed up to the nose, I think.
7.) You can breathe through your nose!
8.) They seem to go through their gas (e.g.: air, nitrox) a bit faster vs. standard scuba mask.
9.) The 2nd stage is integrated with it, so we needed to use a 1st stage from another regulator with it.
There are other brands & models of FFM, and at least one of the Kirby Morgans lets you detach the 2nd stage and accept a buddy's without taking the whole thing off, if I recall correctly. FFMs tend to be rather expensive. Some have the option to add wireless communication modules, but that adds its own complexities.
Richard.