Yep. Any type of thought you have that intrudes on your awareness and sense of happiness/calm is considered an intrusive thought. They can come in many forms: violent, perverted, existential, etc, etc. Any weird thought that causes anxiety and a "woosh" sense of fear/panic/dread is an intrusive thought. The best way to ease and eventually eliminate these types of thoughts is through CBT. Recognize the thought, label it as an intrusive thought, don't try to push it away, don't try to answer it, don't go into the thought (which is called thought entanglement), just let it be. It's a thought. A thought is a thought is a thought.
I read something recently that made a lot of sense. Picture thoughts like little balls of energy. They just fly across the "sky" of your mind. However, when we pay attention to any one of these "flying" thoughts, it brings them closer and closer until that's all we can focus on; we can no longer see the sky. This also can be said about feelings/sensations/etc. Ever have a headache and that's ALL you could think about? Man, my head is killing me, this headache won't go away! But then you get busy doing something and it goes away on its own without effort? It's because you weren't focused on it anymore. Think about having a headache again and boom...there it is!
We are what we focus on. If you focus on the fact that you feel unreal, depersonalized and disconnected, it's all you're going to be able to think about. If you focus on the existential thought of, let's say, humans (why do we look the way we do? why do we exist? how do I know I'm real? humans are weird.), you're going to panic over the thought and how weird humans are and it's all you're going to think about.
Refocusing your attention and labeling thoughts (of any kind) as just thoughts will go a long way. Obviously, this isn't an overnight thing. You're not going to say to yourself "yep, DP/DR is just a focus issue and these existential thoughts are just thoughts...boom, I'm now cured!" It takes diligence in training your brain that, hey, yeah, these thoughts are fucked up (sorry for the language), but they are just thoughts and deserve no more attention than the thought of "that cat is really cute" or "i'm feeling hot".
In the world of OCD, they call it "sticky mind". During times of high stress, fatigue and anxiety, our minds become temporarily "stickier". This means that a thought, feeling or emotion is more likely to "get stuck" and creates a cycle of fear and anxiety over these things.