Do you rap on a cell phone often? Not all cell phones are the same, and some folks run their brains hard, and in addition, hold electromagnetic radiating instraments very close to their frontal lobes. Interferance can occur, as well as brain damage.
How is your diet? Are you eating well? I mean, are you getting enough fiber and fresh foods in you (fruits and green leafies)? Are you well hydrated? Blood isn't too thick, is it? Are you on any wigged out pills that are supposed to enhance memory? Any synergistic effects going on?
Are you drinking too much sugar, booze or caffeine products?
SLEEP. Do you sleep well? Are you giving your brain the chance to process the information that comes from a hard day at school (and then some) via a full sleep pattern, with some nice dreams thrown in as a reward? Are you smoking pot? Are you taking time out for yourself, and rewarding yourself for your work?
Don't phreak out right away. Your normal working brain has various ways of turning on warning lights if you are taxing it. Re-evaluate your support systems, get adequate rest and diet going, and see what happens. If you have all your support systems in order, and you are still drawing a blank during conversations and stuff, then go to a doc. Take care about that. Don't let it go for more than a week, if all your support systems are functioning well.