I think you may be right Charmion. My sister says the same thing. When her young husband dropped dead suddenly at 36, and left her with two little babies, she found that letting out her grief, not holding it back, helped her somewhat to cope. Obviously, loss of a cat isn't in the same league as losing an adored family member, but the mechanism of grief is probably the same.
It's strange how a trigger can set it off - particularly music or a certain song. I can only hope time will heal.
I'm very sorry about the loss of your dear father and your lovely ginger cat.