Unclear questions lead to hazy answers. Your question is very unclear.
Different manufacturers have different 'rules' regarding flash behaviour, so first which camera.
Then, what in the world is PASM mode? You do realise that they are separate settings, I hope (P, A, S & M)
If you're in Manual mode, activating the flash doesn't change your shutter speed or aperture. In other modes, depends on lighting situation, manufacturer and mode.
Pls be specific.