A mild concussion is caused by a blow or jolt to the head.

How and when you feel sleepy has to do with your sleep/wake cycles. These cycles are triggered by chemicals in the brain.

One way that scientists measure sleep is through brain waves, which change in specific ways as you move through the sleep process. Your brain waves change during 4 basic stages of sleep.

Dizziness and a spinning sensation (vertigo) are classic symptoms of a vestibular balance disorder. These disorders can strike at any age. But they are most common as you get older.

Herpes meningoencephalitis is an infection of the brain and the tissue that covers it with the herpes simplex virus.

Chikungunya is caused by a virus carried by mosquitoes. The disease was first found in Africa and Asia, but recent outbreaks have been in the Caribbean and Central and South America.

Lambert-Eaton syndrome is an autoimmune disorder affecting the areas where nerves and muscles connect. It causes weak muscles, trouble walking, and other symptoms.

Uterine prolapse is a condition in which the muscles and tissues in the pelvis weaken. This can cause the uterus to drop down into the vagina. It can cause symptoms such as urine leakage.

Chagas disease is caused by a parasite. It is transmitted to people through the feces of insects. It is common in South and Central America and Mexico.

A liposarcoma is a rare type of cancer that develops in your fatty tissue. This type of tumor can grow anywhere in your body. Common places include your abdomen, thigh, and behind your knee.