Its remarkably easy to have things happen which will stop the flash. Perhaps:
a. the shutter speed crept above 1/180s and you didn't notice (happened to me more than once)
b. If the flash is not locked down against the hot shoe, its possible for the flash to creep slightly out of the hotshoe, not enough to fall off, but enough to disengage the hot pin from its contact. (happened to me more than once)
if either of these conditions happened, and you inadvertently fixed the problem without noticing - it'd be a mystery.
If your system is working now, then thats a good trend