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.