Could it be that your co-workers are seeing you, rightly or wrongly, as some kind of threat to them? For instance, if you were obviously working harder and putting in more time than they were, they might be concerned that you were making them look bad by comparison, and/or setting a standard that they'd soon be expected to live up to.

From the way they reacted this time -- "throwing you under the bus," as it were -- it sounds as if the organization might have been a little on the dysfunctional side to begin with. If only one or two of your co-workers had found themselves unmotivated, just plodding along, putting in their time and trying to do the minimum that was expected of them, they'd probably want to keep a low profile lest the rest of the group turn on them and demand more. If almost everyone there was feeling unmotivated, though, I can see how they might want to turn on someone who seemed to be rocking the boat.

I hate finding myself in a position where I've promised more than I can deliver. It seems even more unfair if I've correctly assessed what I could reasonably be expected to provide and then several unreasonable things get in my way and throw me off stride. I used to get into situations like that a lot; I thought I needed to keep practicing and practicing until I got good at handling them. I found, instead, that I prefer to avoid them almost completely. On rare occasions I may still pull an all-nighter (or the equivalent) when it's necessary to making something happen on time, but I never promise up front that I'll make it happen even if I have to pull an all-nighter.