It is not a pleasant experience, but it is something that has to be endured fearlessly. Fear will only magnify the energy that is being directed at you, and thus prolong the attack. The best thing to do is to remain calm and let the energy have its intended effect. Sadly, once an attack is underway, from experience, it can only stop when the servitor, or egregore, that has been created and sent your way, has run out of the energy it has been created from.
A psychic attack is a real occurrence, it is not something that is imagined. It is basically a menace in a magician's daily life, because there are always those out there who choose to misuse, and waste, their own life force on these rather disappointing pursuits.
Once the attack ends, just as suddenly as it began, it found there is always a feeling of peace and calmness immediately after the attack. By focusing, not on the negative aspect of the attack, but on the experience of the attack, it is possible to avoid suffering any long term traumas related to being violated in this way. Quite often it is not possible to know who is the creator of the servitor, or the initiator of the attack - perhaps we are not meant to be know. Perhaps it is not a human entity that has caused the attack, maybe it is something more sinister.
All we know is that the best way to avoid any similar attacks in the future is to mentally analyse the moments preceding the attack, for any clues as to recognisable trigger points or tell tale signs an attack is imminent. Perhaps it is then possible to have some kind of mental or psychic alarm bell to become activated next time a psychic attack occurs. Remember, however, psychic attacks will always dissipate as they only have a limited energy ... remember also that it is technically created from the life force/thought form force of the attacks initiator. If there are numerous attacks recognised as belonging to the same initiator ... it means it is literally 'killing' them to keep attacking you in this way. They will always come off worse than you if you calmly let the psychic attack run its course.