Thinking...thinking...what would this describe?  What memories, what event?

It feels like all energy is sapped, all but completely spent, as though a battery has wound down, as though each beat of the heart struggles, as if each pulse falters before it manages to pound.   The whole entity dithers and trembles and the brain jerks.   Coldness forms on body parts, ears, cheeks, the tip of the nose, lips, the shins but the knees burn.  The mind tells me crisis point.  You must lie down, be still, be quiet, breathe.  Calm -