Train Extensively, Got Breathing Difficulty, Back Pain On Deep Breathing. Muscle Spasm Or Something More Serious?

I train extensively so am use to minor muscle pulls, tweaks, etc. I had a kickboxing session yesterday evening and it went as usual with no painful impact to any area. I slept well, but once waking up and officially coming to my senses I realized I was short of breath. However, I wasn t short of breath like asthma or as if I just finished working out, I simply couldn t take deep breaths because of the pain it was causing my back. It s been about 14 hours now and has only become worse. Deep breaths, coughing, sneezing , etc. are causing severe back pain . My pain threshold is pretty high considering I train in Mix Martial Arts and compete regularly. With so much on the internet I m just concerned it could be anything as simple as a muscle spasm triggered by the breathing or just coincidental and be more serious like pneumonia or PE, etc.