It must be a high level Doctor thing. When I play my little level 30 Doc, I just watch the team window. If I see 2 or more members taking damage, I check the chat window to see who is really getting attacked. Those damage shields can really mess you up.
And it would really be nice if the puller for the team wasn't an agent who insists on going invisible and expecting you to follow him. I almost lost him twice because I couldn't follow him. And of course, when you can't see him, you can't follow close enough to heal him. After the 3rd or 4th close call, he finally took the hint. Things went much better after that.