brain cramp

noun1

1. •
   (figurative) A temporary mental lapse, such as an inability to remember something, to focus one's attention, to understand something, or to perform some other mental task of which one would ordinarily be capable.

   • "I can't remember. I've got a cramp of the brain. Do you mind hitting me over the head?" "What for?" "To make me forget the last two minutes, and take away my brain cramp." — 1944