A lot of what /u/ItsSilver said is accurate but I have more of the classic symptoms of the illness. It basically comes down to the fact that I can't control my emotions. I am lucky to have learned to hide them well and that anger isn't something I feel any more than most people.
Mania is the defining characteristic of the illness I would say. You have an inflated sense of your abilities and confidence. Some people hallucinate like a person with schizophrenia would. I personally feel like a super human, everything I see has a higher meaning, I am destined for great things, I am brilliant (technically I am, when manic, extremely sharp, creative, and essentially 'brilliant'). It is also a time in which you are likely to ruin a friendship. What happens is your brain kicks into overdrive, producing a huge amount of chemicals to superclock your brain. Like constantly revving an engine, something is bound to go wrong, then you crash. I myself do not reach full mania without some sort of drug activating it, specifically steroids for my back or infections, and SSRI antidepressants.
The crash. Crashing off a mania phase is catastrophic for me, I've only done it a few times but there is about a year of my life I remember almost nothing of it was so bad. I go into an emergency life support mode, I can't handle any responsibilities, my living area, body, and relationships are neglected. Life is miserable, you enjoy nothing, you feel nothing but suicidal thoughts, and you accomplish nothing. This isn't your typical depression or anxiety everyone seems to have these days, it's crippling. After a crash I am prone to what they call 'mixed states' when you are both manic and depressed at the same time. Picture it as getting stuck in the mud with your car, you're flooring it, whipping the steering wheel back and forth trying everything to get the stupid thing to move. You smack the steering wheel and gun the gas in frustration. That's what it's like, you can't escape, you're stuck, and there is no hope in sight. This is when most commit suicide, 1/5 are the numbers I've seen.
Most of my adult life has been in a state of depression regardless of the good things in my life. The mild Hypomania (fun as hell) and Mania (fun for a bit) are not too common in my life. I am very lucky that I cope well with the illness, there are many others that do not cope well and have it much worse than I, not being able to keep a job and are in and out of hospitals.
If you have any other questions feel free to ask, sorry for the mess of writing.