I don't remember whether I prayed Isha yesterday, there is an equal chance or whether I did or did not..

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

Scholars held different opinions regarding doubts about performing a prayer after the expiry of its prescribed time. Some of them held that the person is obligated to make up for that prayer because he had not performed it in origin.

The Hanafi scholars maintained that one is not obligated to make up for a prayer that he doubts whether he had performed it or not, after its due time ends. Other scholars held that the person should act upon what he believes to be most probable.

However, it is more prudent for you to perform that prayer in order to act upon the safest of the different opinions of the scholars, to clear yourself of liability with certainty, and to be on the safe side unless you suffer from satanic whispering. In that case, you should simply disregard such whisperings and pay no attention to them. The optimal treatment for such whisperings and obsessive thoughts is to totally disregard them.

Allaah Knows best.