Amitriptyline is a tricyclic antidepressant that, when taken at a lower dose, can help with the sleep disorder and the pain associated with Fibromyalgia. I had been on it for nearly 10 years, since before I was diagnosed. 
Struggling with restless nights (losing 50-70 minutes a night to awake/restless times), I asked my doctor what else may help and he suggested I increase my dosage. But I didn’t want to do this.
I also wanted to be sure it worked, I had a fear of being stuck on it forever, without really knowing it worked. It was also a scary proposition to go off it and not sleep.
I sucked up the fear and started my experiment in November 2015 and tapered off by 5mg at a time. In the reductions from 50mg down to 30mg my sleep actually improved. But the fatigue increased, I became very fatigued and struggled to stay awake during the day.
By the time I got to 10mg at the beginning of January 2016, I was sore, sensitive and (more) exhausted. My sleep was light and it was difficult to get to sleep and back to sleep when woken.
On my first night completely off it, it took a little while to get to sleep, I slept deeply (I think, I didn’t take my Fitbit on holiday) from 12-6.30am and then my son got up. I was exhausted and sore.
As I continued it took longer and longer to get to sleep, except for the few nights when I was so miserable and exhausted I fell asleep fast and slept like the dead.
I tried 5-HTP and SleepDrops and lavender massage oil. I tried keeping the same bedtime routine, hot baths and no caffeine after lunch. I tried meditation, yoga and any pillow set up possible.
I was experiencing more wide spread pain, near constant headaches and worsening fatigue. I wasn’t coping.
I went back onto 25mg of amitriptyline and had a big sleep on the first night. And a normal sleep, albeit with a six hour block on the second night.
Within a week I was back to getting to sleep well, sleeping restlessly (mostly due to pain), but getting (a broken) eight hours. This doesn’t seem like a win, but it’s the same situation as before with half the dose of amitriptyline, which is a win. The headaches have mostly receded and the generalised, all over pain has quietened. The fatigue is more manageable.
I can only conclude that amitriptyline is working for me at the moment and I am happy enough with that. It has a valid place as the base of my wellness plan.