loosing oil pressure

I have a 96 Dodge ram pickup. With 128K miles

Today on the way to work, i noticed my oil
pressure guage all over the place.
Staying at 40 for a few minutes, then dropping down
for just a few seconds. Then back up to 40.

I recently did an oil change, but dont see how i could have caused
this problem in doing so.

Any suggestions on what it may be?

Thanks for any help, Brad

check the oil again see if your low. check the wire from the sending unit (could be loose)as well as the sending unit it's self (it is a ground sending unit so if you have a amp probe or a volt meter you can see if it jumps up and down)if you check that out and it's fine buy a new aftermarket guage and see what the oil pressure is you can get them for $20-$30. if it's still dropping it could be the oil pump pick-up screen is dirty. but to check this you have to drop the oil pan.