Xanax and doctors

Was prescribed this for insomnia. 5mg no problem, which is why I asked for a bigger dosage. 10mg makes me "happy" and then tired and then sleep, always with dreams and almost always nightmarish (scary) which diminish into weird and once awake am left groggy. I now take Ambien with no nightmares or after effects.

I had back surgery sevral years ago & now need another. Then I had a major heart attack & had heart surgery. I live on pain medication for my beck & take a handful of pills daily for my heart. I am only 47 years old.
I have had problems sleeping for sometime lately have been very stressed. My Doctor put me on Xanax about 2 months ago. At first I slept & felt well but lately I feel overly emotional. I will cry over anything or nothing & just have this feeling like I'm going to die.
I'm wondering if this is a side effect of the Xanax.