Nissan Altima 2004 wont accelerate?

My nissan altima wont accelerate above 5mph, it was driving normal until last night, I turned off the car for a minute an restarted it an it was ok for about a minute then it did the same. Im not an expert about car does anyone have any advice what it could be? I am going to take it to my mechanic later in the week when hes available.