Senior Moment Or What-----HELP ! ! !

Maybe you know where I'm coming from, last night at the Berks Club I played my first two tunes early evening, but when I got half way through my third tune much later in the evening, I went completly blank ! I never had a clue what came next.
.......What can I put that down to ? A Senior moment / too late at night / loosing the plot / going of my rocker ?
.........Have you been there........If so tell us about it, so I'm not on my own
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