How likely am I to gain 20 lbs back? ?

okay I am 5'8" 146, as of 2 days ago I was 148, and I was wondering how healthy it would be if I kept up at this rate until I got to 128. I don't starve myself, just exercise a lot and eat fruit and veggies. however recently I read that if you lose a lot of weight quickly, you are likely to gain it back if not more. can you give me advice or a prediction, please? thank you!! :)