How is it possible that i gained 4 lbs in one day?

Has this happen to anyone?

Sure has. Water and any kind of fluid consumption can add weight. It's not fat weight, just weight. Scales don't discriminate between water retention and fat loss.

Ive gone up or down 2 lbs in a couple hours if I believed my WW scale. I use the scale as a guideline , not a lifeline. You might choose to stay off your scale and go by how your clothes fit.

Thanks i stress about the scale, and you are right my clothe is alot looser.

I usually will "gain" 2-4 pounds during a couple hour bike ride...and thats my goal now. But I will drink 10 pounds of water or more during longer rides.

I weigh myself before and after most all longer exercise sessions....just to make sure I'm not getting dehydrated.

Easier said than done, but don't fret over the daily fluctuations...It'll drive ya crazy.