The death of a colleague can be a painful experience under any circumstances, and is all the more difficult if it is unexpected.
You probably have spent many hours with this person, and consider them to be not just a co-worker, but also a friend. People who work together can become like extended family, and when they suffer a loss, friends and co-workers can also grieve.
Grief can leave everyone feeling a mix of emotions such as shock, anger, denial, guilt and sadness. It can cause disorganisation, negativity or apathy at work. How it is managed will make a big difference to the grieving process. It can also touch on your own fears about death or ignite grief from a personal experience.