Hi RJS,
What you are going through with your injuries is no picnic, and I understand your concerns regarding recovery/spreading symptoms which others like Littlepaw can help you address.
I was formulating a response while reading Littlepaw's comment about further info in your other Post, so I found that one, too.
I understand Chronic pain, many here do, and it can be an uphill struggle to find the right balance of pain meds to allow relief/quality of life. Give your new ones a chance, rarely do things take full effect immediately. Work with your Pain Consultant to get the levels YOU need.
I am also a cardiac problem sufferer, and yes, this adds to the stress and worry we have, especially if one is 'good' like you. I do not know the side-effects of Gabapentin regarding the heart, I had a severe allergic reaction to one tablet years ago when prescribed, but a quick Search should give you answers there.
Talking of stress and worry, you mention you are already Depressed. This is an all-to-common condition for Chronic Pain sufferers, and is the subject I find most important here. Depression makes everything worse, the pain, our outlook… It rarely goes away without some form of treatment, be it Talking Therapies or meds.
Have you discussed the way you are feeling with anyone? Family or friends, your GP or Pain Team (over here PM Teams sometimes have Psychologists/Counsellors)? If not, the Forums can be a safe place to start discussing Depression. Or I'm sure any member you connect with would be willing to converse via Private Message if you so chose.
I am here if needed.

Dave.