Hi to all.
First, I thank you all for the wonderful contributions and insights you brought to my practice (and the problem I was facing).
It appeared that the "damage" implicated the formation of some nasty knots in the upper trap. I did 2 dry needling sessions and some manual therapy (plus, my wife was so kind with me that she did 2 massages a day for me - morning & evening in that spot - for a few days).
I do hope the problem is gone. Today I will resume training, I will start with body-weight mobility drills & naked get-ups & kb dead-lifts and hope that the problem will not return.
On a related note, I remembered I read something in S&S book about the formation of knots deep into the muscle. In the "Chapter Speed Endurance is the answer" is this little gem, and I think overlooked it and created this problem:
"When your reps slow down, it is the best indicator your IIA fast fibers have had it, and slow type I fibers are doing most of the work. This is bad new for several reasons. First, you are no longer improving your power endurance [...] Second, you are more exposed to injury. [...] Third, once your slow fibers have been pounded, they easily go into spasm, exposing you to injury, compromising your training and the quality of your life.
Interestingly, muscles with a high ratio of slow fibers tend to congregate deeper, next to the bones. And slower fibers within any muscle tend to be deeper in the muscle. These two pieces of trivia should give you a hint as to why it is so hard to relieve some knots with massage and foam rollers—they are hard to reach. Do not create the problem in the first place.
These three reasons should be enough to convince you to exercise discipline and stop when your swings are about to slow down—not when something gives out."
Power to all!