I have been using synthetic oil in my car since.

I have been using synthetic oil in my car since I bought it, and the person I bought it from said they ran synthetic since the day they got the car. I had my oil changed at a local business that has done it before (and have my previous records that I use synthetic). They accidentally used non-synthetic oil. They told me it would be fine and that they were "positive" it doesn't make a difference. Now my car is running terribly- it barely started, and when it did start, it stalled. Could using the wrong oil make a difference in how my car runs, or do you think there may be a different issue?