Yes! You definitely can!
Don't worry, you're not crazy
I see "shadow people" all day everyday. In fact, tons of people do! and they're not crazy either! Although, I see a lot more than just the shadow people, but you get my point.
I, personally, suffer from psychotic anxiety. Literally the moment I start to have bad anxiety, I get psychotic symptoms. These are things like hallucinations (visual and auditory), delusions (mostly commonly delusions of persecution), and intense paranoia. What happens to me is, I have anxiety. Once that anxiety has been established it grows. Quickly it becomes very hard to ignore and when I've hit that point, I start having hallucinations.
My hallucinations aren't anywhere near as bad as someone who has intense schizophrenia or something, but they're still awful and scary. The worst part is, they like to hide themselves. What I mean by this is, there not easy to distinguish as real or fake. I have had very intense hallucinations in the past when I think I went through psychosis or something. Anyways the hallucinations, delusions and paranoia were on a totally different level during that awful 48 hours.
I was seeing people that weren't there (like I always do) but they weren't a "wire frame" or like an illusion/hallucination that I usually have. No, these people looked like any other person - it was the scariest thing I've ever had to experience. But the thing about them is - I could tell they weren't real because the way they moved was "robotic." That's actually what made them so scary to be honest. They looked and sounded like real humans, but there movement was totally off. This made them look like robotic humans or fake people which made them incredibly creepy.
There facial expressions looked "animated" and so did there behavior. A great comparison is how the human-like robots in this video look.
Because they looked just like a human, that was scary, but the scariest part was the fact that their facial expressions looked just like they do above. It was awful and I hope I never have to experience that again. But what was comforting about this experience was, I knew they couldn't be real and even though they were standing there, plain as day - I knew they didn't exist.
The hallucinations I normally have aren't anywhere near that intense, however, they're bad because I can't even tell if they're really there or not. For instance, when I get psychotic symptoms from anxiety, I instantly keep seeing people and faces (95% of the time it's just faces) of people out of the corner of my eye. So I instantly turn and look and then there's nothing there. But then when I look away again, I see the illusion of there existence. So it's literally like my mind is interpreting objects as faces when it shouldn't be.
The same thing happens with sound. One of either two things happens. If there is some sort of white noise in the background, I can swear that I hear people talking in that white noise. But I can't tell if it's real or not because it just sounds like white noise. If there is no sound at all, I'll do the same thing but with sudden noises. Like if my stomach makes a sound and it's totally quiet - I will think that sound is actually coming from some where in my house unless I hear it again - only then will I realize it was my stomach.
Sometimes, even if there isn't any white noise or sudden noises, I'll think I can hear people downstairs walking around anyways. But the sound is so incredibly faint, I can't really tell if it's there or not. Obviously there isn't - my mind was just making up sound, but that especially can get pretty scary.