I have a 6 year old Yorkie Poodle mix and he keeps secluding himself while my family and I are in the next room. He will go into my room and crawl under the bed and just lay there. It started happening out of no where. He's eating fine, pooping fine, and drinking a lot of water. We haven't made any changes in the home and we play with him all the time. He used to be so energetic and always wanted to be with us but now he doesn't and it's worrying my family and I.

You haven't asked a question, so I will assume that you want to know what is going on with your pet. I would like to be able to tell you but it is rather impossible on line to do so even when an OP has physical attributes to tell us.

I would suggest you take him to the vet for a blood work up and general exam and go from there.

Dogs that have an increase in water intake could very possibly be diabetic or suffer from kidney failure.

Bloodwork is needed to rule out these illnesses or pinpoint what it may be.

I found this interesting article to consider.

Pampering Your Older Dog | FamilyCorner.com®

And

https://designerdoginfo.wordpress.com/tag/older-dog/

Remote possibility that someone hurt him, family, guest, child, anyone, and he's afraid. Are there kids who might have been rough by accident?
Other than the water question (too much water, or just right?) there's pain. Dogs don't cry in pain unless it's truly excruciating and someone is touching them.
Yes, I'd take him to a vet! Even just feeling him all over the right way to look for spots that might be hurting.