There's times in the gym, where my mind will take my body where it didn't want to go. At other times, it's best to listen to my body. When I hear my shoulders popping and I have a feeling of general weakness, or a runny nose, I know it's time to slow down, and go lighter with my weights. I warm up with light weight, and progress to heavier loads, only if my body allows it.
Injuries are common when we overtrain. Often, I do exercises that are new to my muscular skeletal system. i awaken new muscle fibre and get joy in other ways, attaining the "pump", while guarding against injury. The abdominal muscles are usually the ones that everyone hates working. In reality, these are the most important. Lower back and ab strengthening are paramount in having a good exercise routine. They are the core, and from the core comes everything else.
So listen to your body. Work what needs to be worked. Eat what nourishes you completely. Get enough sleep. Often you will grow stronger with rest.