Mom's Nightmare

I have been reading the stories on this website for a few months now and have noticed a few with the same types of experiences that my mother had.

I study the paranormal and the occult, and I have seen many odd things. My mother and I are both blessed with certain abilities, such as sensitivity to paranormal energy, glimpses of future events, etc.
As stated before, I have seen many odd and unusual things, as I have taken a more studious approach to the unknown;but I have never spoken with anyone else who has had this type of experience.

This particular experience befell my mother several years ago. I was around the age of 6 or 7 (I am now 25) and we were living in a small trailer in Corryton Tn. My mother was married at the time to her first husband (not my biological father) and very unhappy. He was a schmuck and an inconsiderate lout of a human being. (This may or may not be relevant).

One night, while she lay in bed, she was awakened to the sensation of being lifted by the back of her gown. She opened her eyes and found herself hovering several feet above the bed. She felt the sensation of a malevolent presence, so inherently evil that she was unable to put the feelings it evoked into words. She struggled vainly to get out of the unseen grasp. She was finally able, after long moments, to scream for her husband. She screamed as loud as she possibly could, but he didn't even stir. Then, as suddenly as the "attack" begun...it ceased. She was dropped roughly back onto the bed. She blacked out for a moment and then awoke again. Her heart was pounding and she shook her husband, who awoke immediately, as he was a light sleeper. She told him what had happened and he dismissed it as a nightmare.

She disagreed. She felt herself being lifted. She felt the fabric of her nightgown supporting the weight of her body. She felt herself hit the mattress. And most importantly, she felt the unbearable presence of evil.

I know that such an occurrence can be discounted as a nightmare, but my mother was convinced that it was not. And judging by the fear in her eyes when she told me what had happened, I am convinced that it was not either.

Any ideas on what the presence might have been? Please let me know.
Thanks.
(As a side note, there were no other paranormal occurrences in that trailer, or that land as a matter of fact, because we built a house on the same acre several years later and all was normal.)