We are what we focus on. I could focus all day on the fact that I think everything feels unreal and what if I don't exist or am living in my own imagination? But then when I think of something else or focus on something else, the thought is gone until I think about it again.
I've been implementing CBT to any and all weird/existential/DP and DR thoughts I'm getting. Whenever a thought pops up (omg, everything around me looks weird. I'm freaking out...how does the human brain work? how do I know if my memories are my own, now I'm over analyzing words...nothing makes sense!, etc, etc, etc I could write about them all day), I just stop, realize "hey, it's just one of those intrusive thoughts again." don't get caught up in the thought, don't answer the thoughts, don't analyze the thought, just leave it alone. It's just "one of those types of thoughts". Even the thoughts I get "well, why do we have thoughts anyway? why is one thought any better than another?" I stop and say "yep, another one of those intrusive thoughts again. oh well." and go on.
Work is also fantastic for keeping us busy. When I was 17 years old, I was plagued by violent intrusive harm-o thoughts and DP/DR for five months straight 24/7. Thought I was going freaking nuts. That summer, I got myself a fast-paced job and everything went away. It was like night and day for me. It's all about refocusing your attention. Part of the reason I'm stuck in this shit now is because I'm a stay-at-home mom with no available car during the day, no funds for daycare and no job. So, the best I can do for now is try this CBT method. But once I can get a job (my mom's retiring in about 10 months and she's already told me I can use her car if I need to go to work), I'm doing it...not because I want to work 30-40 hours a week, but because it's essential to my mental health.
Best of luck to you!!