2001 Nissan Sentra question

Electrical problem
2001 Nissan Sentra 4 cyl Wheel Drive Type unknown Manual 150000 miles

I was driving the other day and was in 5th gear. The car just all of a sudden stopped running and slowing down. The rpm thing was shaking. I pulled over and the car would not re start. I had almost a full tank of gas. A few hours later the car restarts and seems like its fine. What could be wrong? My father in law suggests a fuel pump or fuel relay but I would liek to make sure befoer spending a lot of money to get something fixed.