Personally I wouldn't see a doctor unless you were getting physically ill from not eating right. For instance in 2002 I lost 25 pounds in a month and if I were say 200 pounds that wouldn't be a problem, but I was 137 and dropped to 111 (I'm 5'6"), because of not being able to eat (I'd be hungry, but after taking 2 bites I couldn't even swallow without feeling like I was going to gag) - it all stemmed from worrying about a weird thing with my eye. My stomach then got upset ALL the time, very nauseated all day long and I COULDN'T eat (the not eating CAUSED the stomach to get upset like that - gas, acid, etc). THAT is when I went to see a doctor. So it all depends on your starting weight and percentage of weight being lost. Like I said 25 pounds was almost 20% of my body weight lost in a month, that is not healthy. If you are 200 pounds and lost 10 pounds in a month you are fine, if you lost 10 in a week, not good.