I have frequently had the vigorous fermentation take place within about 48 hours of starting and mellow out, especially if you had higher temperatures. Remember, your vigorously fermenting wort temperature will be 4-10 degrees higher than your ambient air temperature so if you first day was in a room at 68 you could have very well been fermenting in the mid-to-upper 70s. Overall, I would say that a short vigorous fermentation is pretty normal and nothing to be concerned about. Considering that you've attempted to "revive" the yeast and it didn't make much difference I would guess that the yeast is simply onto the last bits of fermentables and just moving slowly now. If you're really concerned than taking a refractometer or hydrometer sample would be in order.
An example would be an esb I recently did that went into my garage with a ground and ambient temperature of ~55*F, the beer was fermenting between 65-67*F.This was a carboy sitting on cement so there should have been decent transfer of temperature from the ground.
Lastly, just because it doesn't look like anything is still happening does not mean that it's isn't. Yeast do the bulk of the work as fast as they can and the remainder is slow and steady. The airlock can't always be trusted