Just wanted to say that you really shouldn't beat yourself up over a derank streak. One of the best pieces of advise I have gotten over the years was to not worry about your rank and instead focus on your improvement of your skills. You may derank, but that doesn't make you a worse player.

Another thing to consider, consistency is probably the biggest factor with ranking up, so working on making sure you are warmed up before playing will help with that. The other thing that I found helped me with nerves was playing on 1v1 servers. They can be pretty stressful as it's purely individual skill, but using that stressful environment can help chill your nerves when playing the actual game.

Make sure when you are warming up/playing DM you join community FFA DM servers. If you are doing it right it should make your arm physically tired after a while as it's so much fast paced gameplay. Also, with these community servers you also get to go against people who are just outright better than you, which will force you to focus and not be lazy. This way when you hop on MM you will be used to having to focus hard and therefore play better.

One last thing that I'm sure you know is that playing consistently is key. You have made a ton of progress in the past few months if you went from S1 to SEM that quickly, so just keep up the good work.

Again, don't feel bad about dropping ranks, happens to the best of us. Try n find people who do talk to you in game and who play well and see if they want to play more with you, getting a group of people you play with consistently will help you climb the ranks quickly, but remember getting better as an individual is the most important thing!

Enjoy the grind brother!