It doesn't actually "mess" with your mind/emotions. I would say that starting out in Reiki, one begins to "fix" whatever is wrong with what you think and feel. Let me first clarify that everyone has a different sense of right and wrong and Reiki will help align those thoughts and feelings in accordance to you, your inner self, etc. The practice of Reiki often initiates one's search for his/her true self. So as you practice the techniques described in Reiki upon yourself, it may cause you to reflect upon your current situation and challenge what you may currently believe to be right... or wrong. What feels good.. what feels bad... It has helped me rid myself of unhealthy relationships, but I didn't know they were unhealthy before. Yes, sometimes it can feel like hell so it may appear that it messes with things, but actually it's just sorting them out. Try to remain detached during this transition process and always think positive. There is a lesson to be learned in every experience.
good luck I hope you enjoy whichever class suits you best.