Is my cat grieving?

[KeathS]

1. My pet's name is Ruta, age 18, sex M 2. Neutered 3. Grey and white cat 4. Approximate weight 13LBS? 5. What's their BEAM (behavior: newly lethargic and hiding under bed since death of our other cat, appetite good, mood seems sad and confused) 6. Diet fresh cooked turkey, salmon, cod, halibut and Stella and chews carnivore cravings and Greenie treats and pet honesty calming treats 7. Vaccination history: on regular allopathic vax schedule / exposure to toxins: LA Fire air, flea meds behind shoulders bi monthly, other medication: flea meds 8. His companion cat of 13 years died from cancer 2 weeks ago and then he got in a fight with his neighbor friend on Wednesday and now he is hiding under the bed and acting depressed. 10. Has any diagnostic work been done NO? previous Diagnosis mild kidney disease ) 11. Current and previous treatment none 13. @Dr. Christina @Dr. Jeff @Dr. Jean Hofve @Dr. Christina

I am looking for support for my 18 year old cat who seems to be grieving. Do cats grieve by hiding? Appetite seems okay, he just seems depressed and wants to hide. he also did just get into a fight but does not seem to have any wounds. I am giving him flower essences and energy work and lots of love.

Any help is very welcome.

Keath