Hej! While we are of course no doctors, and like @Cornelia Holm and @Joakim Engberg have mentioned before, the safest route to go with your back is to see a physiotherapist to rule out any more severe injuries. I might be able to clear up some misconceptions about the deadlift. It is actually pretty „hard“ extremely injure yourself. Not saying it is impossible, but very unlikely. The spine is very adaptable when it comes down to stretching and being able to withstand force. If you are not a complete bloody beginner and load up your barbell with 100‘s of kgs trying to exceed your bodies capabilities by far, you most likely will not have any severe damage on your spine because of „bad technique“. Especially due to the fact that you would probably not be able to move that kind of weight from the floor properly. Most of the studies and „scary“ stories regarding injuries and disc slips/herniation come from relatively older studies on spines from dead humans and dead animals. A big difference to a living spine and the adaptability of the human body. As a general rule, the heavier the load - the more your back and technique will go into a sort of fishing rod pulling. Of course that is still to be done with proper care and only what your body can handle. you should never experience pain while exercising! What I think happened to you, is simply tense muscles and muscles that are overly strained. Small fun fact, the muscle itself does rarely hurt itself, due to the nerve endings being in something called the „Fascia“. The fascia is like a net laying around and going through your tissue in your whole body. The fascia tightens up when it’s strained therefore - tightens the muscles too and then you experience nerve pains and other type of pains.

As mentioned by the others before, shadow boxing, mirror work. During Covid time many coaches even uploaded padwork YouTube videos, where they will imitate combinations drills for you.

I do follow Phil Darus Heavy Hitter Plan, and some of his others.

@Filip Lernå Can you specify at what situations exactly you would like to work on keeping the punching hand up?

@Filip Lernå This could be a center of gravity issue, i can of course only speak out of the perspective ,regarding stance and techniques, from a boxer. Lets say you bring your hip forward and lean your head back, your arms and hands will instinctively move forward to maintain balance and not fall over. Same thing the opposite, bring back your butt and hips, slightly lean forward your upper body, your hands and arms will go tighten up closer to your chest/head to maintain balance and stability. Regarding doing longer combos I would definitely use the tips that @Leo Kadiric and @Zvonimir Kralj wrote before. When it comes to the going back after you hit someone, could it be that you get a bit off balance after your initial attack? or do you straighten up your legs and hips too much getting out of a low stance?