In general, cycling is very safe. Of course you have to keep your eyes open, but unless you're weaving through cars, doubling the speed limit, or texting, you probably won't have any problems. I see old ladies cruising in Brooklyn all the time, and they're doing just fine.
That said, there are a few things you can do to stay alive on the commute home, because well, cars can kill you. (The whole "high-viz" argument has recently been discussed, where retired cyclist Chris Boardman said he wouldn't support high-visibility clothing and helmets because it focuses on the symptoms and not the cause of cycling accidents.)
Point taken, but it doesn't hurt to do what you can in order not to be hit. And now that it's winter, you're probably going to be doing a hefty amount of riding in the dark. Here's a roundup of the things that can help you avoid incident.