Tiredness

[Mid Life Crisis Marathon Man]

This is what was happening to me last year. Turned out to be viral, and took months to shift. But I'm sure there are less dramatic explanations; e.g. a night on the grog... dare I say especially the champers. You did mention on another thread having been in the pub all afternoon?!

Losing a cricket match can have a similarly debilitating effect.

The fact that you managed 45 minutes after a day on the piss tends to suggest you don't have too much to worry about!