I get flashes of pressure in my neck and increased heart rate. I am going to see a cardiologist next week. What might cause this?

Tachycardia . There are many different possibilities for these symptoms. The cardiologist can evaluate for any cardiovascular reasons. If that checks out ok, there still are other reasons to consider such as a problem with metabolism, thyroid, hormones. This could also come from things people do to their bodies such as not getting enough sleep, too much caffeine or alcohol or drugs. See your doctor foevan exam.