How can I learn to enjoy being busy (see details)?

In the past, stress has always had a way of making me very ill. I have developed a bit of a phobia of being overscheduled, because I tend to get stressed out (and therefore ill) when I have too many committments.
I therefore approached my first year of college very delicately. I didn’t join many clubs for fear of being overscheduled; I was careful to seek out plenty of quiet time to myself to “recover” from the stress of school.
I’ve since had surgery, and stress shouldn’t have such an extreme physical impact on me anymore. So, I don’t want to approach my return to college the same way. I want to be involved in the community, I want to get the most out of it, I want to be busy. But I am feeling a considerable amount of anxiety, because I don’t picture myself being able to adapt to such a change of pace overnight.
What advice can you offer to help me learn to enjoy a busy life, rather than viewing it as stressful and anxiety-inducing?