Well, your post is missing a few points, but understandable due to the dose. 220 is the max heart rate - if you are or have been substaining a high rate of say 170 for more then an hour or two. Its worth heading for the docs. If your rate is slowly going down, you should be ok. However, I am not a medical professional - this is more common sense. At least it is quick acting, so should be out of your system sooner then the XR.
But, to get to another point. I don't know what kind of a doc you are seeing- but NO doctor I have ever run across would start at a high dose and work down. The golden rule is go low and go slow. I hope you just misunderstood your doc.
Please let me know what happens.