I will start by saying that I can relate to EVERY word you said...and I was on 200 mcg's for four years. So, Hi.
The chest pains you're experiencing, is w/d related. I know it all too well, I went through it too..and I went to the ER because, I was concerned that I might be having a heart attack too....and mine was on the left side...It was awful....I AM glad you got it checked out though first, like I did. Unfortunately, all the w/d s/s just need to go away on their own...and I'd like to say, that since you don't have the patches right now, I'm not sure I'd go back up to the 25's myself...you're already on your way to being off, and going on the 25's at this point, probably won't even take away the symptoms.
I also experienced the other s/s you mentioned while taking the med...but I was able to deal with the constipation somewhat by taking Docusate Sodium......the sweats were so bad, just so bad.....so was being hot all the time....I hated that....I also experienced lethargy and, depression....now that I'm off, things are way better, and I find, that although I thought my mind was working at the time, I have amnesia for alot of the time...family will bring up things that happened, and I have no recollection for the events...it's a very powerful drug, not without benefits, but there's a high price to pay for them....
I weaned off the med, coming down by 25 mcg's each month, I had been having minor w/d s/s all along on the med though, like after two days on the patches....and when I weaned, by the time I got down to about 50 mcg's, I started to have them more and more...then came the 25's...I went into full-blown w/d. After two weeks of it, I just stopped it finally, because they were not helping anyway...so staying on them another two weeks and going to the 12.5's was not going to help either. It was very rough for a while, very rough....BUT I made it with the support of people here, and a strong will to succeed. I lived through it, despite feeling like I wasn't gonna, or that I didn't want to sometimes....you can get off of them and be ok, you really can...if you'd like to talk more, you can private message (PM) anytime, ok?
Jacqui
Good job on the taper and good luck. Fentanyl is tough to kick. Chest pain is quite common.