a riddle

Slowly, you blink your eyes. They feel heavy, the exhaustion of the never-ending days weighing down on them. I sit on your lids like royalty; this is my Kingdom.

Looking around, you struggle against me to remain observant, conscious of your surroundings. The colors begin to blur to an iridescent haze. This is what happens when you ignore me -- when you attempt to defy me.

Everything’s futile, of course. However, I am necessary. You cannot avoid me. I am what comes to you late in the night. I knock on your window, and sometimes you may choose not to let me in.

Even though you might not think it, I am here for you. I wrap my arms around you in a tender embrace to keep you safe. I give you reprieves from the world every now and then; I am what you use to escape stress for hours at times.

Pleasurable desires or intimate fears -- I can bring along either during my visits. I come and go as I please, and I bestow upon you energy for when the next day comes.

What am I?