Stages of Grief and mourning?

What are the stages of grief and mourning? and How Many are there?
I heard on friday that my friend from high school died 3 weeks ago. Friday was 4 days after her funeral. I was invited but i didn't receive the invitation until Friday.
On friday I was pretty much giggling over it like "OMG Suzanne's dead. Suzanne's dead" and "OMG she also got married and has a kid" On saturday and sunday I just couldn't stop crying. I barely got any sleep. I took some sleeping pills to fall asleep. Now I just feel weird. I don't feel like crying yet I don't feel like I'm finished mourning.
I haven't spoken to this friend in 4 years. What other stages are I'm suppose to go through?

her death was sudden. she died in a car accident.
We haven't spoken for 4 years because after high schol she went to the community college, I went to the university. We just forgot to exchange contact information after graduation.
I found out 3 weeks later partially because her family didn't have my contact information. Several friends tried to contact me using classmates.com and myspace but I was too busy from work that I just didn't read them until Friday.

I think part of what you're feeling the frustration of not knowing of her passing until afterwards, not feeling a part of the funeral. If you knew her parents, siblings, try to talk with them, or other school mates you had. It's ok to laugh about the good times you had together. We don't know the answers to why we're here, why we are taken. Mourning is a personal process. My grandma died when I was 19, and when my cousins sent a CD of pics it came all flooding back like it was yesterday - I didn't realize how much I missed her, how much she influenced my life (I'm 54 now).

Elizabeth Kubler-Ross details them this way:

Denial (this isn't happening to me!)
Anger (why is this happening to me?)
Bargaining (I promise I'll be a better person if...)
Depression (I don't care anymore)
Acceptance (I'm ready for whatever comes)

She wrote a book titled On Death and Dying.. it is one of the best I have seen.

You will not always go through all of the stages and not in any particular order. You may go through one stage only to return to it again until your healing is done in that area.

Best of luck to you.

First off, I am sorry for your loss. I heard rumors that a friend of mine had passed away a few years ago. It wasn't true, but I still grieved for him. I want you to know that your behavior is perfectly normal behavior. It may seem odd, but this is how you process your grief. You can expect more behavior changes such as denial (which is probably why you were laughing), anger (at her for dying, at God for taking her), depression, bargaining (asking God for one more day with her, or her life in exchange for yours). Finally you will come to acceptance. Acceptance doesn't mean the pain goes away, but you are no longer in the emotional roller coaster you are in now.

Sorry to hear about your friend..from your question it seems as if the death was extremely sudden although im confused as to why you did not hear of this in the 3 weeks between her death and the funeral. Im also concerned about your degree of response given that you had not spoken to her in 4 years. It may be that you have issues with her that you never resolved.
There are 5 stages of dealing with loss
Denial: which at its most basic is where you pretend that the death did not happen or that the death doesn't bother you
Anger: anger either at god, or the circumstances surrounding the death( if she was sick being angry at the doctors for not being able to help, or her family for not telling you on time, or your friend for not giving you the chance to say goodbye)
Bargaining: this is the trickiest one to explain but basically you feel like if you had done something differently your friend might still be there
Depression: this is pretty self explanatory. you may however also experience feelings of guilt- for not saying goodbye, or for not spending enough time with your friend or for being alive when she is not
Acceptance: this doesnt just mean that you have accepted her death but that you have made peace with it
Now you may not experience all of these stages and you may not experience them in the order i have described. You may be angry then be depressed then be in denial. Acceptance, true acceptance, will always be the final stage though.
I would not advise you to take any sleeping pills, it will only blunt your grief temporarily and losing a couple of days of sleep for a friend will not do you any harm.
Talk to her family, get back in touch with them, visit her grave..all of these may help you move on