Martha, I am so sorry for your loss and all you've been through. Your suspicions are right that this new behavior on Prince's part is emotional. It is most likely not just a result of you not paying as much attention to him. Everything in Prince's world has been upset, and I suspect it has finally become too much for him. He has chosen this way to show his own distress. Sleeping excessively can also occur when a cat is grieving. From his viewpoint, first a member of the family suddenly disappeared. Then he was moved to a new home, where the remaining family member is depressed and perhaps a bit distant. Cats are very sensitive to our moods, and I'm sure Prince is confused by all this. A behavior change is one way a cat has to show unhappiness, fear, or confusion. Since you are grieving yourself, it can be very difficult for you to help Prince.
One thing that may soothe him a little bit without much effort on your part is to get a Feliway Diffuser. These are plug-in dispensers that diffuse a calming feline pheromone. They can help cats with a variety of emotional issues or stress. You can also get the product as a spray that you can place wherever you want it, but that has to be regularly refreshed. The diffuser provides a continuous supply. I would put one in the room where Prince spends the most time. You can read more here:http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=8906
You might also try some ways to get Prince to be more active during the day to use up some energy. If he reacts to catnip, give him a new catnip toy. If he likes to play, but you don't have the will or energy, check the pet store or online pet supply merchant for interactive toys. There are several here that don't require a human to play, such as the 'Peek-a-Prize' :http://www.drsfostersmith.com/cat-supplies/cat-toys/ps/c/3261/1897
Of course, best of all would be for you to play with him, but I understand that may be too difficult for you right now. If there is a family member or friend who Prince likes, perhaps you could get them to come and spend some time with him as a favor to you. Here is a site that has tips for helping cats deal with grief or stress:http://woodruffrdah.com/grief-in-cats-how-to-help-a-pet-that-is-grieving/
At the end of that article you'll see that they mention antidepressants. If you think that would help Prince, you could discuss the possibility with your vet.
If you need anything else, don't hesitate to ask. I'm here to help.