Reaction Delayed

What is it with the delayed reaction? Is it a coping mechanism, or what? Like, when you go through something traumatic, and all the while horrible things are happening, but you get through it like a champ, and people are like "wow -- she's tough", and then after its over, maybe 2 or 3 weeks or months after, then you get sick. Or you sleep for days. Or you somehow finally feel whatever it was you went through. You react. Its very strange how these things happen. And I don't think it only happens with bad things, I think it happens with the good as well. Perhaps we're just not equipped to handle all that much stuff at the time of it occurring? For instance, I just found out I got a new job, so I went to my current boss and gave her the news. And then nothing happened. Like Nothing. There was little to no reaction. It was eerie and strange. Then, the next day, I think she's accepted it, or came to terms with it, or something, and I finally did get the "we're gonna miss ya" and "you'll do great there" stuff I had expected the day before. And that was cool, and nice, and yet at the time when she said those things to me, I myself did not react -- it took me a day or so to realize what she said -- a delayed reaction to a delayed reaction --- oy vey.