Cognitive Dysfunction Syndrome (CDS): The dog's age, history of OCD behavior, barking at the sky, and recent onset of pee accidents inside are consistent with CDS, a common condition in older dogs that affects their cognitive function and behavior.

Gastrointestinal Disease (e.g., Inflammatory Bowel Disease): Weekly vomiting for 7 years suggests a chronic gastrointestinal issue that may be contributing to the dog's overall health problems.
Allergic Dermatitis or Skin Infection: Red, inflamed skin under the fur could be due to allergies or a skin infection, which is common in dogs, especially those with thick coats like Chow Chows.
Arthritis: Stiffness when getting up, although not severe enough to prevent walking or running, could indicate early signs of arthritis, a common condition in older dogs.
Dental Disease: While not directly mentioned, dental issues could contribute to vomiting and should be considered, especially given the dog's age.

Hypothyroidism: This condition can cause skin problems, weight gain, and stiffness, among other symptoms. Although not directly indicated, it's a critical diagnosis to rule out due to its potential impact on the dog's quality of life.
Cushing's Disease: Another hormonal disorder that could explain some of the dog's symptoms, such as skin changes and potential increased thirst and urination, leading to accidents in the house.
Neoplasia (Cancer): The possible lump on the neck is a red flag for cancer, which is a significant concern in older dogs and could also explain some of the other symptoms if the cancer has metastasized or is affecting various bodily systems.

Neurodegenerative Diseases (e.g., Degenerative Myelopathy): While less likely, these conditions could explain some of the dog's neurological symptoms, such as barking at the sky or OCD behavior, especially if they are progressive.
Autoimmune Disorders: Conditions like lupus or rheumatoid arthritis could potentially explain a combination of the dog's symptoms, including skin issues, stiffness, and possibly even gastrointestinal problems, although they are less common in dogs.