Accelerator not responsive

Nissan 2006 Altima.  Driving down the road and all the sudden the accelerator does not
respond.  The engine does NOT go off though.  The first time it happened I just coast to
a stop and I put it in park. Before coasting to a stop I shifted to neutral and tapped the
gas and it revved. Shift back to drive and nothing.  Once it coasts to a stop, I shift to
park.  Then after about 10 seconds all lights in the vehicle completely went off (even
emergency flashers), but the engine is still running.  After about 45 seconds all lights
come back on, i put it in drive, the accelerator responds again and i take off.  No
problems for about 3-4 days.  The second time it happened i shifted into neutral again
before coming to a stop and tapped gas and the engine revved.  I then shifted back to
drive and hit the gas and the accelerator responded again and i took off.  The lights did
not go completely off in the second episode, but they dimmed and when the gas pedal
once again responded i noticed the lights got brighter and the AC got louder.  Again,
the engine never dies during either episode. Took to the shop after the first episode and
he hooked up to diagnostics, but no codes came up.  Any thoughts?