Felt like I was going faint/pass out, why?

For the second time in about a two week period, I faint/pass out. The first time it happened, I was in the middle of what ended up being a nearly week long migraine; I was sitting in a rocking chair and started getting a tightness in my stomach, then my breaths started to sharp and shallow, and I started to feel faint. My roommate yelled up to me to ask him a question, and I could barely get an answer out. Tonight I had exactly the same thing happen, except I am not having a migraine. What is causing this to happen? I will say that I recently started taking Excedrin Migraine (acetaminophen/aspirin/caffeine) to stave off an ever increasing frequency of migraines, however I have found the Excedrin to be very effective for relief. I took one tablet this morning because I felt a headache starting to come on, and wanted to get on top of the pain before it got worse. Now, I have taken acetaminophen for years with no issue, but I do not drink any caffeinated beverages, and have only taken aspirin maybe three times my whole life. Could it be the aspirin or caffeine that is causing this to happen? I also take an opioid narcotic called buprenorphine on a daily basis. Any help with this is appreciated.