Transferring to another department

Does anyone have experience transferring from one department to another? I've been in my ER for about 4-5 years now and I'm exhausted. The workload is extremely difficult and I really want a change. There is a sister hospital very close to me, part of the same medical center, and I'm interviewing there on Monday. They are an ER but way less workload. I'm nervous about "why I want to transfer there". How do I emphasize how much I love my job but the need to change without offending or angering anyone involved?
I'd find a way to say something like you are looking for new, stimulating experiences because although I totally get and have worked like a dog on some units that just can't be stated diplomatically in an interview, imo. Good luck!