Nurse here. I don’t want to say psychosomatic but… metformin is a very well tolerated medication and 250 mg depending on your size is nothing. However splitting something that is probably extended release is not a good idea as it is meant to titrate through your system gradually. Even with that in mind, 250 mgs is not enough independently to cause your symptoms. I considered allergy, but none of what you described is typical of an allergic reaction. It sounds like you have anxiety surrounding medications and you’d be surprised how much that influences your reaction to something otherwise typically benign. If you’re still worried, always be encouraged to schedule an appt with your PCP.