All:
I've brewed numerous batches of beer and lots of mead and I've never seen primary fermentation seem to be done this quickly.  I brewed a 5 gallon batch of English style nut brown ale Sunday night.  It was a partial grain kit from True Brew with all English ingredients:
1 oz Weyermann roasted barley, 6 oz crisp pale chocolate malt, 6 oz crisp crystal extra dark malt, 3.3 lb can light hopped LME, 1 lb light DME, 1 lb amber DME, 2 lb dark brown sugar, 1 oz Fuggles hop pellets, 6 g Munton's Ale yeast.
I put the wort in the primary about 2200 Sunday night.  The wort was bubbling like a witches' cauldron by 0400 Monday morning and continued with very strong bubbling through the early hours of Tuesday morning.  When I got up this (Tuesday) afternoon the bubbling was very slow and the air lock popped only about every 10 seconds.  Looking into the beer with a bright light (glass carboy) just now, I don't really see any bubbles forming.  The air lock hasn't moved for at least an hour.  Could it already be done with primary fermentation after less than 48 hours?


 

It could be finished, but the only way to tell is to take a hydrometer reading to see if you have reached Final Gravity. If it is the same reading for 2 days consecutive and within your Final Gravity range, it's finished. Don't be in a rush to bottle, give the yeast time to clean up after themselves to give a cleaner tasting beer.

if all conditions right, could be done. but best to check as poster above said

What are your fermenting temps? A cold spike can put some yeasts to sleep. Try to rouse the yeast by giving the fermenter a swirl and wait. Sometimes it just is finished fast, only your hydrdometer will know. Check you expected final gravity and compare to your readings.

If it is done, it is done!

Some British yeasts can really get after it sometimes - but only to about 85% final. Then they drop-off and go very slowly for the last 15%.


Heed this warning! Many times, in their vigorous fermenting, the yeasts will throw off some serious off-flavors and smells. Make sure you give them a few days to not only finish the fermenting (it may look like nothing is happening, but they're still working away), but to also re-process some of the off-flavor & aroma "waste".

Just sit back, relax, have a beer and let it sit for a few more days. No need to rush good beer.

Fermenting temp is around 69 degrees.  I plan to let it sit in the primary for a week or so, then rack it into the secondary with a clarifying agent.  As is there is a ton of particulate matter floating around.

You can cold crash it to drop the particulate before racking to secondary which will help a lot.

I racked this brew Monday night.  Looks and smells great.  I went ahead and carbonated a pint with our Soda Stream.  Worked like a charm.  Yummy stuff.  Potent for a brown ale due to the extra pound of dark brown sugar I added, but not so much as to make it taste too "boozy".