Delta brain waves are the lowest frequency of all the brain waves. They are associated with deep sleep, unconsciousness, and coma. Delta waves are usually less than 4 Hz. Some people report feeling a sense of euphoria or well-being when they experience delta waves. Others have described them as feeling like they are in a trance-like state. It is important to remember that everyone experiences brain waves differently and that there is no one "right" way to feel them.