Should I be worried about an internal tickling sensation in my chest? I have only felt it while sitting or laying down in bed, particularly after taking ambien. I feel like itching or pounding my chest/back to relieve the feeling but it doesn't help. Also

As above. To be sure it is always better to see your PCP for evaluation and work up.
It. It is difficult to fully answer your question without more information. This may be an adverse reaction to ambien, (zolpidem) but it might be something else. This chest discomfort does not sound like angina, which is exertional chest pain as a result of narrowings in your heart arteries. Although this is not exactly what you are describing, some heart conditions cause fluid accumulation in the lungs that results in difficulty breathing or cough at night when lying down to sleep. You should discuss this symptom with your personal physician. Or, stop the Ambien (zolpidem) and see if it goes away.