US-04 Imperial Stout Stuck?

My first all grain batch... A big Russian Imperial Stout. 6 gallons

Recipe is as follows:
12lbs 2-row
1lb chocolate malt
.5lb rye
1.5 lb crystal 60
.75lb roasted barley
1lb of plain table sugar

Cooled to 70* and pitched 1 packet of US-04.

Within 12 hours it was bubbling away. Within 18 hours I had to use a blowoff tube because it was going NUTS. Bubbled all night long like that.

I came home from work this evening, 48 hours after pitching, and the blowoff tube isn't bubbling the water at all. Not a bit. I realize that no airlock movement can be insignificant, but considering that it WAS moving significantly and now it isn't, I'm concerned and not sure how to proceed. Any advice would be greatly appreciated.

If it all works out, I'm going to just let it sit for a couple of months, add 12 ounces or so of espresso made from some home-roasted coffee (my other hobby) and have a nice, big, one-at-a-time winter ales to keep me warm through the holidays.

Check the gravity now, then check again in a week. If there's no movement, you may have a problem (unless it's already done..) - if there is movement, check again a week later, etc etc.

Airlock means nothing, gravity reading means everything.

Big beers require big patience, grasshopper.