After using Myo-Fix Concentrate for a couple of weeks, my skin started to feel numb. Is it normal?

Yes, this is perfectly normal. As peptides works on the muscle fibres intertwined with the skin, you may experience somewhat strained sensation and being less able to move your facial muscles in the areas where you applied concentrate. This can be accompanied by slight numbness which will pass when you finish your active course of Myo-Fix. Usually this occurs after 4 or 5 weeks of using the concentrate, sometimes a bit earlier if your skin is more sensitive than normal.