Blew a puff of smoke for about 20 seconds

[Virginia]

Weirdest thing happened. I pulled away from a green light and heard a fairly loud lifter rock. I looked in the rear view and saw a big cloud of smoke. I lasted for about 20 seconds while I was accelerating and then it just stopped and hasn't done it again. My oil pressure looks good and the temp looks good. When I got where I was going and could look around the truck I noticed oil dripping but the trucks been leaking oil forever. This is the first time I could actually see it dripping though. When I came out it had quit dripping. The puddle was about the size of a dessert plate. I drove home. No rattle and no smoke and no oil dripping.

 

Any ideas?

[jtdesigns]

valve stuck open maybe??

[Virginia]

What might cause that? And how do I keep it from happening again?