Bear with me... (Wyeast 3724 question from first-time user)

Pitched 2 packets (from May, I believe, had been swelled at room temp for like 4 days before I remembered 'em, then put into a 1 L starter for brewday) of 3724 into a 1.056 wort with 12oz table sugar, and the rest DME, and some pils malt (mini mash). Pitched at 7 pm last night, by 11 pm had an occasional blip from the blowoff tube. Woke up this morning to the blowoff tube covered in scum and a healthy, vigorous fermentation with a bubble from the blowoff about every second or so. Left the beer at around 80 or a little hotter all day and came back...fermentation is much more subdued now (looking into the Better Bottle) and the bubbles are only ever 5-6 seconds or so. I know that airlock/blowoff activity isn't really representative of what's going on, but since this is my first time with this yeast, I'm nervous. A few questions:

1.) We left the (east-facing) blinds open this morning to get the room up from the low seventies to around 80 or 82. Could the cooling of said room (i.e. the sun moving around to the back of the house) have caused enough of a temp swing to sort of stall this yeast?

2.) Is it more likely that, with the amount of yeast I pitched and a relatively low-gravity wort, that she's just done her thing much quicker than I expected her to, and is now just entering that famous 3724 lag phase? I figured I'll take a grav. reading tomorrow and see where I'm at, but I didn't expect it to shut down this early (my other recent beers went through 1.5-2 days of crazy vigorous fermentation, not closer to 15 hours).

Help a brewer out?