What does a nervous breakdown look like?
Is it something like an epilleptic seizure?
What causes it?
What are its consequences?

I imagine it's something like a panic attack. Normal faculties of "coping" shut down, and even the most menial task seems overwhelming. But where a panic attack would be a paralyzing state of hightened alarm and agitation, a nervous breakdown would be similar to acute depression. Mechanisms that allow you to make decisions under pressure, such as prioritizing and delegating, all collapse in on themselves and leave you defeated. This would be triggered after prolonged mental stress or sudden traumatic events, especially when support isn't readily available (or accepted).

But that's just how I understand it. According to Wikipedia (http://en.wikipedia.org/wiki/Nervous_breakdown):
Although not a medical term, the phrase "nervous breakdown" is often used by laymen to describe a sudden and acute attack of mental illness e.g. clinical depression, anxiety disorder, etc. in a previously outwardly healthy person. Breakdowns are the result of chronic and unrelenting nervous strain, and not a sign of weakness. Like any machine, the human body will start to malfunction when put under too much stress. However, although in common usage the term "nervous breakdown" does not have a clinical definition and no reputable doctor would use it in serious diagnosis, instead focusing on definite symptoms and underlying causes. One common diagnosis used in this case is brief reactive psychosis.