What Are The Side Effects Of Miralax?

I currently use miralax on a daily basis twice a day and have been for about a year. I am concerned about it s long term side effects it might be having on me. I am experiencing a rapid heart rate, not sleeping well, anxiety and other issues and I don t know if its because of my thyroid problems, throat cancer or is it possible of my prolonged use of miralax and would like more information. Please let me know what you think.