Alcohol Abuse, alcohol, benzo, or opioid withdrawal
Depression/anxiety
Bipolar disorder, schizophrenia
Hepatic encephalopathy
TBI
Acute mountain sickness
Delirium
Hyperphosphatemia
Medications (many!)
Excess caffeine
Sleep-disruptive environmental circumstances
Restless legs syndrome
Sleep apnea
Short duration sleep circadian rhythm disorders
Chronic sleep restriction
Psychosis
Insomnia
Alcohol Abuse, alcohol, benzo, or opioid withdrawal
Ergotism
Depression/anxiety
Sedation 
Bipolar disorder, schizophrenia
Hiccups
Hepatic encephalopathy