Is it true that having too many nightmares can have an affect on your brain such as forgetfulness?

Cause over the past few days i have forgotten things and i even forgot my trainers today whcih i supposed to be using for PE.I'm not usually forgetful but also can be when feeling a bit apprehensive and upset about something;and i'm tired of having bad dreams,i've had alot of them nowadays and for once wnat a decent nights sleep without all these strange and scary images popping up in my head whilst i sleep.Or if i'm gonna have a dream why can't it be a good one and are any of you else experiencing the same thing?