Real angle of attack is made up of two parts, induced alpha and effective alpha. Downwash increases induced alpha thus reducing effective alpha meaning you have to increase real alpha to stay in level flight.
In the ground effect the downwash is inhibited so induced alpha is decreased. This increases effective alpha so you get more lift -bouncing out of the ground cushion - until you adjust real alpha
Coming up out of ground effect the downwash comes in again, induced alpha goes up, effective alpha goes down and you get that sinking feeling.
This can be serious if you are near the stall, so performance figures specify Vr, rotation rate and Vlo (lift off) to keep you clear. Do not rotate too soon or too quickly and you will be ok.