The first signs of a hypo are usually the rapid heart beat, sweating etc which are due to adrenaline release as low bsl is an emergency - the brain is threatened and this adrenaline release ( from the adrenal gland) plus release of a hormone called glucagon) from the pancreas gland both influence the liver to release stored glucose, thus helping to raise one's BSL and imprive the glucose supply to one's brain.
Adrenaline is activating emergency body supplies to deal with an internal or external threat and that can keave one tired afterwards, similar to uf one receives a bad fright or has to fight, defend oneself or escape danger.
Then if the hypo lasts long enough, the bsl is low enough, one's brain starts to suffer and the after-effects can include slow-thinking, mull headedness and tiredness.
The important thing is to try and work out why the hypo happened and how to prevent ot at least minimise it happening aain.
Best Wishes.