Hallucinations involve sensing things while awake that appear to be real, but instead have been created by the mind.

Considerations
-- Common hallucinations include any of the following:
-- Feeling bodily sensations, such as a crawling feeling on the skin or the movement of internal organs.
-- Hearing sounds, such as music, footsteps, windows or doors banging.
-- Hearing voices when no one has spoken (the most common type of hallucination). 
-- Seeing patterns, lights, beings, or objects that are not there.
-- Smelling a foul or pleasant odor.
 
Causes
There are many causes of hallucinations, including:
-- Thrombocytopenic Purpura
-- Being drunk or high, or coming down from such drugs as marijuana, LSD, cocaine (including crack)
-- Delirium or dementia (visual hallucinations are most common)
-- Epilepsy that involves a part of the brain called the temporal lobe (odor hallucinations are most common)
-- Fever, especially in children and the elderly
-- Narcolepsy
-- Mental disorders, such as schizophrenia and psychotic depression
-- Sensory problem, such as blindness or deafness
-- Severe illness, including liver failure, kidney failure, HIV/AIDS, and brain cancer