Chemical imbalance is not something out of this world. When you get excited, angry, sad, or happy; those are all probably a bit different chemically.
Now, the same way you can be sad, and talk yourself out to someone to feel better (talk therapy), many of us would reach for some chocolate instead. It has been proven that pleasure producing things such as enjoyable foods, release endorphins and such, thereby changing the CHEMICAL balance in your brain.
So you can actually change the chemical balance by talking it out, or by eating piece of chocolate. It’s more complicated than that, but it’s a pretty good analogy. Sometimes the therapist will try talk, medicine, or a combination of both…