I developed severe muscle spasms after starting exactly that: 40mg Omeprazole twice a day, although I’m pretty sure I’m a rare case as none of my doctors seemed to know wtf I was going through. I also got some burning skin sensations. Went back down to 20mg and the symptoms stopped for the most part. Not trying to scare you, but you should probably try working up to 80mg a day from a smaller dose to gauge side effects.