There was a time when I was constantly being attacked by an unseen spirit when I was asleep. I would hear a buzzing sound and then I would be rudely awakened by the feeling of paralysis. I would struggle for awhile before I would be set free. There were times I would feel hands pinning me down and there was once I saw a rough white image of a face turning towards me.
I freaked out of course and sought help with my spiritual master, H. E. Tsem Tulku Rinpoche. He adviced me to recite White Umbrella's mantra and keep a consecrated image of White Umbrella next to my bed. So I recited it every day and initially the spirit problem got worse but after that it eventually died down. It was very effective for me and for a few of my other friends. Hence, I always advice people with similar spirit problems to recite White Umbrella's mantra for protection. There's also a White Umbrella chakra amulet if its needed for those who don't want to recite the mantra.
Mantra - Om Sita Ta Pa Trey Hum Phet