Started venlafaxine 4 days ago. been having a lot of issues. been having really bad brain fog, tired to point of almost passing out/fainting during classes, heartburn, more jittery and anxious, numb feeling, can't concentrate. is this normal?

Different people react differently to medications. Contact your doctor as there are alternative medications that can provide the same relief, with fewer or different side effects. Exercise regularly, it will improve you physical and mental health. Wish you good health!

You are apparently having several adverse side effects, and you should contact your doctor about this, as venlafaxine may not be a well tolerated product for you. A different medication might be handled far better.