I myself have been attacked in my sleep, if you read some of my other posts about sleep paralysis you will find some of my idea's and theories concerning what it is.
Seems to me you've accidently crossed through the veil into the astral plane (and not all of it is pretty) and had an encounter with something that
needed your energy, like a moth goes to light, so do these things go for us.
I think this is where there legends of the vampire originally stem from, there are no human vampires as such, but there are leechers (entities that as
you say exist on sub-harmonic levels) therefore not physical in much the same way that a bass frequency isn't physical, you can feel it but not touch
As I say, I encountered it twice in one night a few years back, during a pretty bad experience in and out of something in-between an attack of sleep
paralysis, an OOBE and a lucid nightmare. For me I was terrified and it was feeding off my fear from halfway across the room, the more i tried to
move, the 'darker' it got.
It was something like a long and tall 'man' all in black and was very evil, its very presence made the room darker than normal.
I felt a huge pulse of vibration going through me from my feet to my brain, and a sound like every particle in the air was shaking, a strange electric
buzzing sound and other scarier sounds like distant screaming, the sound of two people talking to each other but the words were indecipherable and an
old style radio voice, plus other weird stuff....
I think the screaming sound could have been me (in my head) but the other sounds were coming from everywhere in my room.... Like this thing carried
sounds with it and its very being wa causing disruption the the air. That's the only way I can explain.
The weird thing is, I felt more 'alert' and 'tuned in' than I'd ever been, like I could hear the tiniest of sounds all amplified and slightly
It didn't get close to me though, instead it mocked me from across the room...
I 'awoke' or unparalysed and I knew the thing was still about, depsite my rational mind telling me it was an hallucination, I KNEW it wasn't...
I then drifted in and out of disturbed sleep and again felt that rushing feeling and awoke to find my housemate standing over me shining a blue cell
phone light into my face and he was laughing... smirking.
I couldn't move but could hear myself shouting at him (wtf! are you doing standing over me etc!) and then the blue light was shining in my face...
I then 'awoke' again and looked around my room and things weren't as bad, whatever it was had gone... my door was locked in the morning.
My housemate denied all knowledge of pranking me (i mean why would he get out of bed, break into my room and shine a phone in my face?)
Very freaky but interesting stuff...
I've had sleep paralysis fairly often since then, but nothing as bad as that attack.