Your brain has just adapted to constant change over time. You're now much older but your neurons have been trained to follow a certain pathway for a long time. So how you feel makes absolute sense. It's all you know. And your brain loves, loves, loves, to make predictions based on previous experiences. Even if it doesn't reflect your current reality.

So, if you want to feel differently, you have to change your thinking pathway. Start by telling yourself all of the time that what you have is here to stay and that you are safe, secure, grounded, and will be around for a long time. Eventually, a new neural pathway will be forged and you will feel like what you have and who you are have more permanence.

Not an expert, but I have been down this road.