I have been going to physiotherapy for 3 months (Yes, I am getting better now. Thank
you for asking). My physiotherapist and I have established and agreed that there are 2 types of pain. One type is a sharp pain that is hurting you badly (in which case you scream). The other type is working/stretching your muscles that somehow (not sure how) it is loosening up your muscles and it is good for you. As a non-medical professional, I am not sure how to explain it technically. But one key difference to me personally is the working pain is the one that trains your muscles within your tolerance (before screaming) and will eventually heal you.
No pain no gain!