Dangers of Heating a Bedroom up to High Temp
You mostly want to protect yourself and pets from harm:

As you can imagine, you do not want to be in the home while it is this hot. Not only does this give the bugs a way to escape by climbing onto you and the going with you when you leave, but it can pose health problems.
Even when you are in a sauna that reaches these same temperatures, you are not inside for nearly so long. You will have to find a time when no one needs to be home for the duration of the treatment if you want to begin killing bugs with heat. If you have the time, this is very much worth it.

Obviously you'll want to remove anything sensitive to heat, such as candles, personal products, and food.
However, you'll need to do a fair bit better than 120 degrees:

Generally speaking, your home will have to be heated up to 140°F and held at this temperature for two hours. Alternatively, you could have the home brought up to a temperature of 130°F and held at that level for three hours.

So 120 degrees probably won't do it. Also, if you're just doing one room, you're probably going to see a quick resurgence of the critters.
http://www.bedbugs.org/heat