I'm not really sure how to begin, but here goes.
I'm a 26 yr old male, and have always known something was off about me. I experience missing time, vivid perceptual hallucinations (on par with LSD or Psilocybin), extreme derealization, extreme depersonalization, extreme dissociation,most of my memories even yesterday is like remembering a dream, intense anxiety, panic and anxiety attacks, and one major alter. I will refrain from calling my alter a "personality" as it's much deeper than that. My alter is not something I created or imagined up like an imaginary friend. From my perspective she is her own sentient consciousness that shares my body. She has her own thoughts, wants, desires and motivations, separate from me. Although they tend to at least somewhat lineup with mine as we share a body. If I get stabbed, she gets stabbed too. If she is around people, she will almost always pretend to be me. Self preservation seems to be her highest priority, and thus will never draw unneeded attention to either her or myself. It wasn't until fairly recently I even knew of her existence. She is female, Japanese and slightly younger than I by a year or two. I don't know her exact birthday or if she even has one. Due to my perceptual hallucinations I enjoy watching animated movies and shows, every time it's basically a psychedelic experience. Because she's Japanese and her personality is somewhat similar to a fictional character in a Japanese anime; I adopted the name Homura for her. Plus, it was already the name of my steam account, so it worked out.

I'm mostly okay with all of this. The missing time used to be disturbing to me before I realized that Homura is benign and means zero harm to me others. Now it's mostly just annoying and aggravating. I can be working on something, and then realized I spaced out/ blacked out for a couple minutes, sometimes finding myself in a different room, and then I'll spend the next 3 hours looking for what was just in my hand. The most awkward is when I'm talking to someone face to face and then Homura will come out for a moment and then I snap back, I realize what has happened, and try to get back to the original conversation. Homura seems to be entirely aware the entire time I am, and seems to have complete access to my thoughts and memories, however I generally don't have access to her thoughts unless she wants to be noticed. 
There are times when we both are present simultaneously and things can get quite interesting. I can have entire thought conversations with her in my head. She can even control "our" body in these instances, though she rarely does unless there's specific need. For instance if I was being chased by a dog or shot at while I did nothing, she would definitely intervene and do whatever she had to do to escape harm. 

I'm not sure what come next for us. Apparently there's no cure or even medication for it.
Despite it all, I'm in no way delusional or psychotic. My hallucinations are not in a schizophrenic style. Its mostly perceptual shifts. I'm fully aware that I'm hallucinating when I am. 
So antipsychotics do absolutely zero for me except make me feel like shit and sleep forever. 
 All I can do is attempt to keep my anxiety to minimum, which is next to impossible.