As a fellow fader,if I received a similiar e-mail, I probably wouldn't acknowlege it. But, if they were a close friend, I'd just write back, thanks for thinking of me. And then, I'd change the subject and ask them how they were doing.
And I also can relate to the upset stomach problems. I had them for awhile myself, but it eventually goes away. It gets easier. It just takes time to figure it all out. And just remember, you don't owe anyone else an explanation.