All of the stuff talked about here can happen really quickly and it can be all mixed in together, meaning that sometimes it's hard to make sense of. It's important to remember that these feelings are to be expected and that they will pass.
Usually the process works itself through and you develop new patterns of living (you still remember the person or thing you have lost but you are able to get on with life without it getting on top of you). However, sometimes people need a hand to deal with grief, like when it's really extreme (causing a major disruption to your life), or if life doesn't get any better after a while.
If this sounds like where you are at, then you should get some help to try and work it out. Hit the help button for some information about people who could help you.