I’ve had laser treatment done on 4 different areas and have had 4 different treatments over the course of 2 years. The place I went to used YAG laser and registered nurses did the treatment. I NEVER experienced what you wrote here (ie. darketing of skin and “hard” hair").
My areas would be red and welted for a few HOURS afterwards and that was it. I don’t mean to freak you out but if I were you, I’d go to a doctor.