You will lose some "skills" as others have said, but you will gain many others that will translate well to the ER. Thinking and acting quickly in an emergency, is a big one that I can think of. Time management is another, as you will often be managing and passing medications for upwards of 10 people. I've worked on units where the med pass was split, each nurse passed meds for 10-12 people, and I've worked on units where there was 1 med nurse for a 27 bed unit. Passing meds for 27 people requires great time management. You will learn how to interact with physicians, as well as work in a pretty autonomous environment, much like (I imagine) the ER to be. You will learn to be a patient advocate "hey (psych) doc, he is pretty out of control, I think he needs a nice dose of (insert your favorite psychotropic here)...OR "hey (medical) doc, I know you hate coming down here and you think all our people are just crazy, but I really think this guy is going into DT's. I really need you to come evaluate him now." (Okay, maybe leave the first part out :lol: )
So, if we are being realistic, (because is it REALLY that easy to just go grab yourself an acute care job and get the "right" experience?), take full advantage of what you have now, keeping the big picture in mind. Try to get a dysrhythmia course somewhere, take ACLS, and when you do get that chance to sell yourself to that ER manager, remember to play up the relevent aspects of psych as they relate to the ER.