No oil pressure. No low oil light on. Was fine last night but not this morning.

Last night I was driving my 2000 Eddie
Bauer expedition. All was pretty normal for
its age.  while driving on hwy the check
engine light started flashing. I parked it for
a few minutes then all was well when I
cranked it back up. When I parked it for the
night no lights were on and all my gauges
were perfect. This morning I went to crank
it , it started right up. But I had no oil
pressure. And the oil light was not on. I cut
it off immediately. Checked oil. It was at
the minimum line. No oil was under my
truck at all. I put two quarts in it. It's
registering on the dipstick as having oil
now.  I did not start the truck back up in
fear of messing it up. But I did turn the key
over to see my gauges and the oil pressure
went all the way up as all the gauges do
and then it went back down to no oil
pressure at all. I even reset the battery.  
Should I try to start it?  How could this
have happened literally overnight while the
truck was off?  I don't know what to do
and it's my only vehicle.