If the car restarted afterwards, the alternator, nor the battery are your problem.

If the headlights died as well, the OVP is not your issue either (their function is not tied into anything the OVP protects).

Most likely you either have a loose connection on the battery posts from the jumpstart (once load is applied and they heat up, they can lose connection) or you have a bad ground strap somewhere. I'd start by checking the terminals on the battery for tightness, then move to check the ground straps on both ends. Both the one that connects the battery to the body, and the one that connects the engine/transmission to the body.

Losing ALL electrical power like that indicates a total disconnect of electrical power (just like a switch as you mentioned). The alternator and OVP are highly unlikely to be your issues here.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]