i suddenly have trouble processing information

i noticed lately my brain has been acting slower than usual. i usually am such a sharp/fast thinker but now my brain is having trouble processing things. today at work, i was told to type a 4 letter code and i kept forgetting and not understanding what to type. and this is not the only time. my brain literally shuts off sometimes. when my coworker is telling me a story, my head for some reason tunes it out and i feel lost for a moment before asking them to repeat the sentence. i’m only 20. i have never been diagnosed with anything. i’m really concerned if this is something serious or maybe stress?