Jellyfish stings are relatively common problems for people swimming, wading or diving in seawaters. The long tentacles trailing from the jellyfish body can discharge thousands of microscopic barbed stingers that release venom into your skin.
Jellyfish stings can vary greatly in severity. Most often they result in immediate pain and red, irritated marks on the skin. Some jellyfish stings may cause more whole-body (systemic) illness, and in rare cases, jellyfish stings are life-threatening.
Most jellyfish stings get better with home treatment, but severe reactions require emergency medical care.

Jet lag, also called jet lag disorder, is a temporary sleep disorder that can affect anyone who quickly travels across multiple time zones. Jet lag is caused when your body's internal clock or circadian rhythms, which tell your body when to stay awake and when to sleep in the old time zone, are out of sync with cues from the new time zone, such as light exposure and dining times. The more time zones crossed, the more likely you are to experience jet lag.
Jet lag can cause daytime fatigue, an unwell feeling, difficulty staying alert and gastrointestinal problems. Jet lag is temporary, but it can significantly reduce your vacation or business travel comfort. Fortunately, there are steps you can take to help prevent or minimize jet lag.

Juvenile rheumatoid arthritis, also known as juvenile idiopathic arthritis, is the most common type of arthritis in children under the age of 16. Juvenile rheumatoid arthritis causes persistent joint pain, swelling and stiffness. Some children may experience symptoms for only a few months, while others have symptoms for the rest of their lives.
Some types of juvenile rheumatoid arthritis can cause serious complications, such as growth problems and eye inflammation. Treatment of juvenile rheumatoid arthritis focuses on controlling pain, improving function and preventing joint damage.