Ambien is not a benzodiazapine. I wouldn't suggest it as a long term treatment for insomnia but for short term use. 5 - 10 days worth should get one's sleep pattern back to normal. I do this myself as one of my warning signs is disturbed sleep pattern so my psych and I nip it in the bud.
The kind of anxiety you are going through happens to many Grads, boy I was twitchy at the end of my last semester. It's really important that you regulate your sleep naturally. Stay away from any stimulants, like pepsi and coffee, even drinks with green tea in it.
Set yourself a strict sleep schedule, make sure there are no "activating" things going on like playing on the comp. or watching TV in bed. (though TV is a cure for my insomnia, they aren't sure why). As well, carbs, like pasta after 7 or so, it will give you energy for 4+hours. It's better to have protein based food instead.
Realize that this can be controlled through talk therapy and have a check up with your doctor. I would never recommend a benzo which is what ambien is to help regulate your sleep, it will bite you back in the long run. It's better to look at an anti-anxiety drug rather then a tranq if possible. I've been on a sleep med (non-tranq) that was originally on the market for depression and I sleep like a baby and have had no withdrawals when I've missed a dose or two. I have General Anxiety Disorder, which is a long term issue, but with situational anxiety there are many more avenues to try. I am in general for meds to help balance a person who's got a chemical imbalance, but I wouldn't suggest it if there are other alternatives, try them.
You are going through a huge transition, they say that graduation is in the top 10 most stressful things next to divorce and getting married! Give yourself a break, breathe and relax, if you over analyze - you'll fret more. If you get a negative thought, realize that it's just a thought, and choose a positive thought or activity. Once you get on track, you'll be stronger to deal with things in the future. You'll be fine, just don't psych yourself out.
Most people are stressed when they reach the end of college. It's a big change in life, going from academia to the work world even in the best of times. If you're not ready to leave you can always go to grad school. Given today's economy, the opportunity cost of spending another 2 or 4 years in school will never be lower.
The only problem with frequent bathroom use is it seems to upset you. Try to relax about it. If you can't sleep, talk to your doctor about it. Use a sleep aid like Ambien until your normal sleep pattern is disturbed. If you have medication for anxiety, taking it before bed may help you sleep.
The chance of you dying at this stage of your life is very small. If you are average you probably have another 50 years to go. I have serious health issues and I have just come to accept death as a normal part of life. Nobody can tell you how much longer you've got to live. All you can do is live a healthy life and hope for the best.