The way I explain the difference between normal feeling experiences and my feeling experiences (with bipolar, major depressive disorder and generalized anxiety disorder) is with color:
Imagine you’re holding a ball. It is deep blue. This ball contains all of your sadness. This ball is 100% of what you experience when you are sad.
Now imagine walking into a room. The walls and ceiling are painted the same deep blue as the ball. This room contains all of a depressed person’s sadness. This room is 100% of their experience when they are sad.
The important part is that the ball and the room are the exact same color, and each of them contains 100% of each individual’s sadness. One is larger than the other, but the sadness is based on the same color. If you have felt 100% of your sadness at some point, you have experienced the same sadness a depressed person feels, only you experience that sadness to the extent that the ball can contain, and they experience it to the extent that the room can contain. It’s the same color, and either way, you’re both at 100%
The room full of sadness causes far more problems than the ball full of sadness. A ball doesn’t take up much room and can fit in a hand the same way a healthy person can fit comfortably into a life. A room cannot be moved unless it is deconstructed piece by piece or destroyed.
Empathy comes down to relating. If you have been very sad, then you know what sadness feels like. You know fear. You know anxiety. The specific chemicals that cause all of these things are in each and every one of us, and they don’t get classified as mental illnesses until they start causing problems in the ways we function. A normal or neurotypical person’s experience of a feeling may reach 100% of what they can handle, and it is uncomfortable, but they manage. A mentally ill person may experience that same level of a feeling as the normal person had, but it’s far from the limit of what they can feel. The person who is mentally ill may experience the total of what they can feel at a level that would be three times greater than what a neurotypical person feels, far exceeding what a human can handle with success. It’s still the same feeling, just at a debilitating level. When it becomes debilitating, it’s a mental illness.
How you empathize with someone’s unfamiliar mental illness without experiencing the mental illness yourself is research. If you want to understand what it is like living with mental illness symptoms, look up the disorder of the individual you are trying to understand, and study their symptoms. The internet is the greatest tool ever invented, and I cannot think of a better use of it than bringing yourself closer to your fellow human beings. There are millions of people with mental illness with blogs and youtube videos, explaining exactly how and what they feel. A five-minute search session will clue you in enough to at least empathize.
Not everyone is capable of handling extreme emotions, but we are each certainly capable of empathy. Do your part as a human by reflecting on how others feel by finding the similarities between them and yourself. We share the same neurological chemical components and the same world. Only our perspectives are separate.
We humans all feel, without ceasing, until we die.