For you, I think it might be a demonic entity planning an attack. he is checking you out. Do you have angels, Holy Angles that visit you, are you protected by the Blood of Jesus.
Can he get at you. Sounds like he is observing you right now.
What emotion, other than scared do you feel? Scared because it is unknown, and you are anxious to interpret and protect yourself.
Sleep with a small night light, do you still sense this presence.
When you are tired, you can hallucinate. And varying shades of black could be linked in your imagination and interpretted as a form.
I don't think this is the case though, because you said your mother saw it too.
There is a whole spirit world around us. Most of us can't see it, especially in our waking state, which is most likely a good thing.
So to tell you there is nothing there, it is your imagination, is false and a disservice to you.
You already sensed a specific entity.
Now for discernment, is the entity good or bad?
What are you going to do with him. Can he serve any purpose to you. Can you control him. Protect yourself from it, if need be.
It really can't hurt your flesh, per se.
Watch your moods and emotions.
Why are others saying you are changing.
If you do not have the HolySpirit of God in you, available thru Jesus Christ, you can be possessed, and any entity can reside with your soul,inside of your body.
That is how God created it, he said, don't you know your body is the Temple of God. God made us for Him to live intimately with us, joined together, linked spirit to spirit in this body.
He will not intrude, you have to ask God in.
Meanwhile I sense a spirit entity is scoping you out, for a resting place for himself.
You can get rid of him by calling on Jesus.
Peace....