In the game you cannot be Prone while it is your turn at all - falling prone immediately ends your turn, and you automatically recover from prone at the beginning of your turn.
We cannot say whether Larian's game code allows you to attack while prone, because other circumstances of their code prevent us from ever having the opportunity - namely that 'prone' carries with it 'unconscious', so whenever you are 'prone' for whatever reason, you are also 'unconscious', and thus incapacitated and incapable of doing anything at all.
This needs to be fixed, but has been like this for along, long time and despite numerous reports has not been corrected yet.