Keeping rooted in the present in the face of past realities
Do vipassana, a retreat if possible. In every moment you have a memory, know that it is a memory, know about feelings which are coming up and so on. Your mind is in the habit of believing the images, but in fact what you see is just mental noise. Maybe you had past lives like that, but it does not matter (I bet you think it does matter; that's exactly the power these images have over you). The training in returning back to the present moment (by acknowledging whatever is happening and letting it go, time and again) will gradually break the attachment of mind to those images, so you will be able to stay more stable even if these images come.

Whatever in the mind is not a hindrance to be present, if seen clearly for what it is (body sensation, feeling, mind, mind object -- technically speaking); present cannot be destroyed but we are sometimes unable to tune in back to it, and that's why we train.

As a side note: if your condition is psychiatric (you are not able to take care of yourself in regular matters, often can't distinguish hallucinations from reality etc), do seek proper treatment first.