I think you guys just get "people'd out" and don't demand alone time to recharge.
I also don't think you know how to recharge yourselves when you are alone as well as the intp's do...being nt's the intps just have to grab a book or internet with a pet theory to recharge or let their mind wander and embrace their latest delicious cognitive sculpture...you guys may not have such an easy "just add water" solo escape, and since you may feel "bad" just leaving others when it "is time" to do so, you may let yourself get worn out.
My isfp friend emails me when visiting home saying, "everybody is all over me for all kinds of reasons" (meaning they want advice, a listening ear, company, etc.). I told him that when he got home I was going to be all over him for just one reason...that is really all he needed to hear. Being an introvert, he really didn't want to rehash all of it and being an intp I sure didn't want to hear it. Had he been an nf he would have wanted to share how he had psychotherapized them, but as a sensor, he doesn't do that. I recognized that his isfp presence and energy probably did more than any nf's psychobabble could ever do for them (sorry, nf's...but unless you are prof. therapists, all of that is usually unsolicited and more about you).
Anyway...I think isfp's are healthy, not mood swingers...just that they stop short of taking care of themselves so we see what we would all be like if we let ourselves give to that point.
Be sweeter to yourselves and more confident.