Our stories sound so similar. As an only child, I was the sole caregiver for my mother during the last three months of her life. Of course, I treasured that time I had with her and happily did everything I could for her. But, like you, I had a major FM flare following her death. It took me several months to get back to "normal" – even with the help of an excellent massage therapist and acupuncturist.
We know that stress can trigger a flare, particularly when that stress is prolonged. And the illness and subsequent death of a mother can't help but produce stress in us, whether we realize it at the time or not. My personal theory is that when we are facing some kind of crisis, the adrenaline kicks in and we are able to do things we normally couldn't handle. But the longer the crisis continues, the more depleted our bodies become. When the crisis finally ends, we begin to feel the effects of what we've been through.
It sounds like you have a good doctor and are on the right path. I would just encourage you to get extra rest and give your body time to recover and heal. It wouldn't suprise me if it took as least as long to recover as the time you spent using that extra energy. I'm not sure that the flare itself is necessarily part of the grieving process, but grieving might possibly be a contributing factor in recovery time. You will eventually feel better. In the meantime, allow your heart to go through the normal grieving process and allow your body time to recover.
I wish you the best,
Karen