Is it possible?

 Is it possible to gain 4 pounds OVER NIGHT?? I'm up 4 pounds this morning from yesterday morning. The thing is that I worked all day cleaning at a shelter where I volunteer and ate less than usual. I had a 4 oz. protein shake, 1 boiled egg w/ a lf string cheese and 4 oz. of sauteed shrimp and asian vegetables, water and coffee. I'm at a loss here.
What can I do to get rid of this stupid regain?

You did not gain four pounds of fat jus****er gain.  Try to drink lots of fluids today to flush your system and the scale should be back to where you were by Thursday.  I have days like these too.  I sometimes jump up three pounds and I know I have not consumed more than 1200 calories that day.  Looking at what you ate, the asian vegetables probably had a lot of sodium in them.  I know it is frustrating but just tell yourself that the SOB scale is a liar.  You know what you ate!  Have a better day today.

Thank you Tess! I am going to keep drinking my water and do all protein shakes today except for dinner and that will be lean chicken breast and broccoli. Thank you for the support.

shrimp and Asian vegetables - most likely lots of salt.
And working out - the muscles swells (bet you are sore this morning) swelling is nothing more than water retention..