"Forgetfulness" joke

[Not good reading, but good for a group]
An older lady gets undressed and starts to get into the bathtub. She
gets about halfway into the tub and thinks, ''Was I getting into the
tub or getting out?'' She calls out, ''Bernice! Was I getting
into the bathtub or getting out?''
Bernice says, ''Well I don't know. I'll have to come up and look.''
Bernice starts walking up the stairs to the bathroom, gets halfway
up and thinks to herself, ''Was I going up the stairs or down?'' She
calls out ''Sally! Was I going up or down the stairs?''
Sally, down in the living room calls back, ''How should I know?'' and
thinks to herself, ''I'm glad I'm not losing my mind like the other people
in this house.''
So Sally starts...
Do you remember the punchline to this joke?