I don't have an answer for you but I wanted to give you my respect and condolences. I fear this transition coming, too, so I think perhaps I can relate.
Care giving has been your routine for 15 years, so you need to find a new routine. I recommend you begin by going for a walk each morning, even if you need to drive somewhere and walk in a mall. Maybe stop for a coffee. You need some contact with people, but at least initially probably on your schedule. Maybe some volunteer work with a library, hospital, red cross, food bank, church, etc. Start looking for community events you would enjoy: senior center meetings and exercise groups, club meetings, concerts, re-enactments, classes, festivals, ball games and begin attending them. Start reconnecting with friends and family you may have lost touch with during your care giving years; call someone and invite them to lunch. Maybe look for some part time work to fill your day.
Has your mom moved to another place or passed away? You selected grief so I’m assuming she’s passed away, and if that’s correct, I’m very sorry for your loss. It’s been a long while since I lost my mom and I still miss her everyday. It does get better with time, and the tears become more often smiles as the good memories come to mind. It’s a life change for sure, and it’s never wrong to reach out for counseling if it becomes too much. I wish you peace
Be kind to yourself.