Depersonalization is when a person feels they have lost touch with reality, that they are living outside of their body and floating along as if they are in a dream. In this disorder, unlike some other disorders, the person is aware that this is happening to them and this can make it all the more confusing. They feel detached, almost robotic in their day to day life. This  can last for a very short period of time for some, however for others it can last for years.

Depersonalization is different in each individual, some experiencing very mild symptoms whereas others have chronic, ongoing symptoms. The sufferer can become emotionally detached. They can feel due to their condition that they are not in control of their words or their actions at all. They may feel like they are going crazy. This can lead to further complications like depression and anxiety.
The exact cause is not known however it has been linked to post traumatic stress, and to some other personality disorders like depression, and schizophrenia. In some cases there appears to be no apparent cause, or trigger at all.

Depersonalization can interfere with your day to day life, your work and your relationships with family and friends.