High altitude cerebral edema (or HACE)'s a severe (frequently fatal) form of altitude sickness. HACE's the result of swelling of brain tissue from fluid leakage and almost always begins as acute mountain sickness (AMS). Symptoms therefore usually include those of AMS (nausea/vomitting, insomnia, weakness, and/or dizziness) plus headache, loss of coordination (ataxia), and decreasing levels of consciousness including disorientation, loss of memory, hallucinations, irrational behavior, and coma. I… (More on Hace)