This happened a little while ago and I want to write it down so I don't forget.
Fasting is hard for me. In fact, I don't usually do a typical, 24 hour, no food, no drink fast. I have blood sugar issues and headaches and other problems that make it so I physically collapse if I don't eat for several hours. So, I try to modify my fast to either skip one meal, or forgo something I like, like treats that day, etc.
Over the summer, I was visiting my family in Oregon, and while we were at church, a woman made a comment about how she hadn't been fasting for years because of migraines, but then she felt prompted to pray the night before Fast Sunday and ask Heavenly Father to bless her to be able to fast. Since that time, every time she did that, she was able to fast the next day with no problem.
I was floored. It had never occurred to me to pray to be physically able to fast. But as the next Fast Sunday approached, I decided to test this idea out myself. I expressed my desire in prayer to be able to have the strength to fast, and I went to bed. I continued that prayer in my heart the next day, and miraculously, I was able to fast the whole day until dinner, even with wrangling my kids at church and doing everything I needed to do- and no fainting, throwing up, dizzy spells, or headaches. Wow. Not to mention the other blessings I was able to receive by fasting. That tells me that Heavenly Father wants to help us obey and receive all the blessings He has in store for us. (Not that we can't modify our fasting when medically necessary, but if we have the desire to do it, I think Heavenly Father will help us to make it work.)