airlock bubbling, then not

I am brewing a Brown Ale which is about 4 days old now. After 12 hours, the airlock was beginning to bubble and after 24 hours if was bubbling once every 15 seconds. After about 2 1/2 days the bubbling has been significantly reduced and, from what I can tell, it may have stopped. That or I am just too impatient to wait around for it to twinge. Is this a problem, has fermentation halted. Fermentation began at about 72 degrees (which I thought was too high) and is now reduced down to 68 degrees. There hasn't been a whole lot of krausen, at the max maybe an inch. Now there is just a thin layer of broken up, non foamy krausen. Any ideas on whats up?

Sounds perfectly normal... leave it in there for another week and bottle it.

I agree 100% with The Pol, just because airlock isn't bubbling like mad doesn't mean it's stuck or done. Leave it a full week longer then secondary if you plan to, or leave it 2-3 more weeks and bottle or keg.

What you describe is exactly how most of my fermentations proceed.

As many people on this forum will say, an airlock is a poor way to measure if fermentation has stopped. The only way to see, is if you take a hydrometer reading. That being said, even after FG has been met, the yeast still are at work. They are cleaning up after themselves and making your beer taste better. You should probably leave your beer in the primary for 3 weeks before bottling it, just to make sure that it is at its best.