I drink coffee everyday ... w i encounter this problem a lot :
الظاهرة التي تصيب البعض ويعبرون عنها "بأن الكلمة على طرف لساني ولا يمكنني تذكرها
my short term memory is kind of bad
... it seems this could be related to the coffee drinking issue ...
Now I have a difficult choice to do : either quit drinking coffee or continue with this problem !!!!!
mmmmmmmmmmmm i get used to this problem, but i don't think i can get used to not drink coffee 
P.S: for those who have exams, it's better not to use coffee as an alert material, a goodnight sleep is much better than staying awake all night.
Thank You ...