Popping in and out of 1st gear

Hey All. My bike is popping in and out of gear under load. I just noticed it this morning doing my customary Sunday morning off-the-line blasts. I'd wind up the rpms a bit and take off - normally with no problem but today I kept hearing and feeling a clicking and loss of power - like the gears were disengaging and reengaging. This was happening in first gear, but then later in the ride I also felt it happen once while overtaking a car in a higher gear (not sure which I was in, but I was gunning it).
I read a few related threads which succeeded in scaring the crap out of me - sounds I may need to split the cases to take a look. Though everyone seemed to be focusing on 2nd gear - didn't read anything about first (or other gears).
What can I try short of anything drastic?
I happened to be recording my ride this morning - here's a link to the video. Please excuse the cursing.

Chain too loose?
Steve

SWest wrote: Chain too loose?
Steve

Aha! Quite possible. You may have just put the happy back in my happy place. I'll check it out.

Chain is definitely loose. I'll readjust and test again. I'm hopeful it's as simple as that. Thanks Steve!