1997 Nissan Altima Car Problems

I have a 1997 Nissan. I was out driving it around town yesterday and as I was driving (going about 40mph on a flat road) the RPM gage started to freak out and go from 2 to 0 and suddenly my car stopped. After about 3 minutes I was able to start it up and drive on some more, we made it about a mile before it started to do the same thing and died. This time a couple of people were kind enough to stop and help. They offered a jump but the car didn't need it, It started on up, they checked all the fluids (though I have been keeping up on them and knew it wasn't the problem) and nothing seems to be low or dirty. It dies every few minutes -- I can't get far, and if I stop at a light or for any reason I have to keep my foot on the gas to keep the car going.

Any idea what could be wrong?

Thanks in advance!