While there are many ways to understand the nature of feelings, I find that Mark Nepo, in his Book of Awakening, captures the essence of it in a way that brings relief.  It is helpful to remember his words in a moment or period where one is experiencing an uncomfortable section of the range of human emotion.  In my experience as a therapist and as a person, I have learned that a healthy human being can tolerate experiencing the whole range of emotion, not just the emotions that are easy to be with. 

"Not to feel is to stop the heart from breathing

So often, we war against sadness as if it were an unwanted germ, and pine after happiness as if it were some promised Eden, whose gate is keyed to the one secret flaw we need to rectify in order to be worthy...

...Yet it is no mistake that to suffer means to feel keenly.  For to feel deeply and precisely with full awareness is what opens us to both joy and sorrow.  It is the capacity to feel keenly that reveals the meaning in our experiences.

If you are thirsty, you can't dip your face into the stream and say, 'I'll only drink the hydrogen and not the oxygen.'  If you remove one from the other, the water cannot remain water.  The life of feeling is no different.  We cannot drink only of happiness or sorrow and have life remain life.

The truth is, that as the lungs make sure of the air we breathe, the heart makes use of the things we experience.  Thus, to be alive is to feel....To feel keenly is our necessary privilege."