Grief is weird.
One would think that it was a very linear process: you'd feel really crappy at the beginning, then as time goes on, you'd feel better and better. It's simply not the case.
In fact, for the first couple years, it seems to be a reverse process. In the beginning, you're actually doing fairly well. You're in shock more than anything, even if the death was expected. I don't think we ever believe death will truly happen, even if you've been watching it get closer and closer.
You function fairly well initially because there's so much to do. There's simply no time to fall apart when so much planning and organizing has to happen. Of course there are blips when it hits hard, but then you have to get back to getting stuff done.
A few months later, some of that numbness starts to wear off and you start feeling things. Bad things. But at this point, people expect you to be feeling better, not the reverse. You're back at work and involved in activities, and it's hard to explain why you want to take to your bed now, rather than immediately following your loss.
This cycle of normalcy and misery bounces back and forth for a long time. Strange things set it off either direction. I've watched a movie that mimicked my experience without feeling much, then something seemingly unrelated will just shatter me and every raw feeling will be right there at the surface. It's very exciting (not in a good way!) because you never know when it's going to happen. I've started crying while singing Christmas carols. I sobbed every time I saw a trailer for the movie "Australia", though not during the movie itself (a little dull). Other times, I just feel crappy or angry for a few days, a few weeks, and can't seem to shake it.
Having been through this before with my dad, I know that over time it does get much better and ebbs and flows of grief level off, but I also know it doesn't happen for the first couple years. I'll be bursting into tears at inopportune times for a while to come now, but I know it is all a part of the process.