My humble answer: This is a good question for me to answer, because I was on Theo-dur for 25 years, and every time I'd skip a dose I'd have an asthma attack. So I thought I'd be on it for life. The idea here was that once you have a certain theophylin level in your system, your body expects it to be there always. So, if you suddenly stop taking it, your body may punish you the way it punished me.
That is why a slow wean is important with theodur. Ideally, you should work with your doctor on a good plan for weaning yourself off this once popular and now essentially out-dated medicine because of all the aweful side effects.