Metformin and side effects?

Hi everyone. Not sure what I should be posting this under, but seeing as how my wife's weight loss doctor is the one who prescribed Metformin I will post here; hope that's all right.

The situation is this. My wife is not strict on taking her meds at all. I would say she has taken her Metformin once in the ast month (probably 3-4 weeks ago). She was told originally to start at 250 mg/daily for 5 days, increasing every 5 days until she gets to at least 2000 mg/daily. However since she hasn't taken any in a good bit, she should have started back at 250/daily for the five days. Instead, yesterday for some odd reason she took 2 doses of 500mg each, totalling 1000mg for the day. I am personally thinking that this is about 750 mg more than she should have taken yesterday. Also, this weekend her eating was quite bad and unstructured, and very little water consumption (less than a litre for the weekend).

Today she is nausous, has a bad headache, and is feeling a bit dizzy. Also, for a couple of hours she was very cold this afternoon and could not warm up. Could this be due to the haphazard useage of Metformin as well as maybe being dehydrated? She usually gets about 2.5-3 litres of water a day so this was pretty restrictive for her.

Any information would be appreciated. Thank you so very much.