Thanks for reaching out.
Your father is going through a 'grief reaction'. It follows after a perceived or an actual loss of a loved one. It starts from denial, then anger, bargaining, depression, and acceptance. These symptoms may oscillate to and fro. He might be eating less, sleeping less, sad most of the time, crying, maybe experiencing the presence of the loved one around him, lack of interest in things, tiredness, etc.
This may occur for a period of 6 months more or less and usually doesn't interfere with a person's general functioning. However, in this care your father's quality of life seems to be disturbed at the moment, it is wise to consult a Psychiatrist. Depending upon the level of distress, medicines may be prescribed keeping his age and other aspects in mind. He may also get some therapy along with the medication if necessary. He should feel much better in no time rest assured.
All the best.
Dr. Pavani Narukurthi
MD Psychiatry
MindfulTMS Neurocare
Gk2 Delhi
Next Steps
Consult a Psychiatrist online or in person.