You might find it hard to concentrate or stay alert, or you might find it difficult to remember things, like finding the right words when you're doing a public talk that you've had to memorize.
Puede que te resulte difícil concentrarte o mantenerte alerta, o puede que te resulte difícil recordar cosas, como encontrar las palabras correctas cuando estás dando una charla pública que has tenido que memorizar.