I'm assuming by 'the old woman' you are talking about Lady Macbeth. There is also a 'gentlewoman' that goes to see the physician about her Lady because she is not sleeping. If you mean what happens to Lady Macbeth, she goes crazy and can't stop washing her hands because she keeps seeing blood on them. She can't sleep without the lights being on. If you are talking about the gentlewoman, she suspects that Lady Macbeth has done something terrible and she goes to the doctor to have him observe the Lady and see if there's anything he can do to help her sleep or stop washing her hands. Earlier Lady Macbeth claims to have seen a dagger floating before her in the hallway.
