Jealousy, morbid
Preoccupation with the possible sexual infidelity of one partner. The afflicted, usually a man, becomes convinced that his partner is having an affair. Morbid jealousy is often brought on by a personality disorder, paranoia or depression, but can also arise from alcohol dependence or organic brain syndrome.
Jerky nystagmus
A type of nystagmus (involuntary eye movement) in which the eyes move slowly in one direction, then dart back.
Jet-lag
Disruption and fatigue of the sleep-wake cycle, brought on by disturbance to usual body biorhythms as a result of flying through different time zones. Jet-lag causes daytime tiredness and insomnia at night time. More symptoms included reduced mental and physical activity and bad memory. Jet-lag is usually worse after an eastward flight (which causes the traveller to lose time) than after a westward one.
Jogger’s nipple
Soreness of the nipple created by friction from clothing, often during sports such as long-distance running or jogging. Both women and men can be affected. Prevention is by applying petroleum jelly to the nipples before prolonged running.