Problem starting on Hill?

[FcukThis]

Weird things are happening to my yaris... Hopefully they're nothing serious.

About 10 minutes ago, i parked my yaris on a hill alongside my driveway. I ran into the house to grab a few things i had forgotten, came back outside and my car was dead.

Ok, i say to myself. "No problem, Maybe the battery is just dead. I'll just go and jump it".

I flip the car into neutral and begin to lower it to the bottom of my driveway where it is flat. Before i could even back out, the car regains power.

I go to the bottom of the hill and park it, turning the ignition on and off repeatedly to test my battery.. everything appears to work fine.

I drive up to the hill where my car originally lost power, put it into park, take out the keys. Bam i lose power again.

Whats going on?!?! -- I have an automatic transmission. Gas is 3/4 full.