Stop over eating: feeling dizzy


I have been on balanced diet at 1500 cal/d for 2.5 months.
On Monday I switch to overeating advises: I made a protocol that I follow and do 8 hours eating window. I removed flour and sugar.
Today I am feeling dizzy, my brain is slow. Is that normal? I am a bit worried. I work many intellectually so I need my brain working I cannot be in limbo all day long.

Please advise