Benzonatate side effects

This medicine made me extremely jittery and nervous. I had a panic attack and heart palpitations on it which were scary. I think it may have been because I had taken 3 separate doses back to back. It was as prescribed but may have been too much for my system. Now I am done with antibiotics but still trying to get over bronchitis and I don't take it as much, like I save it just for night time when it's the worst (coughing).

blackish stools

I'm not sure, but I would like to know what side effects come with this medication, as my stool has been black and I'm trying to see if it's from the medicaton.

Thank you.