Is it possible to self-diagnose cerebral edema or HACE?

What are the signs and symptoms of high altitude cerebral edema?

• Severe headache
• Confusion
• Nausea
• Vomiting
• Seizures
• Coma

One has to wonder if it is it even remotely possible to self-diagnose HACE?

The short answer is not really. The signs include confusion, seizures and a coma which makes me believe it's impossible to self diagnose HACE.

How likely is it for a high altitude mountaineer to develop cerebral edema when ascending to 18,000 feet by bicycle? HAPE is possible, but I doubt HACE.

Not likely because the ascent is slow and the rate of ascent allows the body to acclimatize. HACE is normally a condition you expect to see in a climber at extreme altitudes and when the rate of ascent exceeds 1,500 feet per day.

High altitude is defined as:

If you can diagnose it then you probably are experiencing either Acute Mountain Sickness or homesickness. Both AMS and homesickness you can diagnose in yourself.

What's AMS like to experience?

"AMS has been likened to a bad hangover, or worse. However, because the symptoms of mild AMS can be somewhat vague, a useful rule-of-thumb is: if you feel unwell at altitude, it is altitude sickness unless there is another obvious explanation (such as diarrhea)."

The diagnosis of AMS is made when a headache, with any one or more of the following symptoms is present after a recent ascent above 2500 meters (8000 feet):

Homesickness is a longing to return home.

Homesickness is the distress or impairment caused by an actual or anticipated separation from the specific home environment or attachment objects. The term is in origin a loan translation of nostalgia, a learned term coined in Baroque period medicine. The Oxford English Dictionary describes homesickness as a feeling one has when missing home. Feelings of longing are often accompanied by anxiety and depression. These symptoms may range from mild to severe.

Here is a good primer on altitude sickness, acclimatization, AMS and HACE.

International Society for Mountain Medicine, An Altitude Tutorial