Is losing 20 lbs in 2 years too much and too fast.is that considered unexplained weight loss? cancer? also is unexplained weight loss a consistent loss or can you go up and down a few pounds?

Unexplained and unintended weight loss of 20 lb in two years would warrant an evaluation, preferably by a GI specialist. A few pounds this way or that is not important, if you did not intend to lose weight. Wish you good health!

If the weight loss is involuntary and not the result of lifestyle changes, it appears significant enough to trigger workup to start with your primary care doc. Some seasonal weight variation is possible otherwise, most commonly involving few lbs weight gain during the cold season that is usually lost during summer.