Loneliness nobody to share life with

Grief. Losing a loved one is very painful and the feeling is with you forever...

Helplessness.

I consider myself a highly self-actualized, independent and resourceful kitty. I don't mind assisting or asking for assistance - but when there is nothing I can do to help a situation, it eats me up, paralyzes me. Especially if the thing is happening to someone about whom I care.

Like a ball of ice in my stomach that won't go away. I hate that feeling.

Regret. You can combat and conquer those other three things. Regret is forever.

Other. Technically, this probably goes in the fear department, but it's distinct enough I think it deserves its own category. I think the worst feeling is cognitive dissonance. When your worldview says the world ought to be like this, but the world is not conforming to that scheme. For small things it's not a problem, but when an experience is telling you that everything you thought was true about reality, might not be... it can be the worst kind of nightmare.

Having felt all of them I'm going with fear. You can alleviate all the other feelings with medications, friends etc. Being afraid and trying to live day today is difficult, especially in these days of new technology where security can be breached easily. Fear of someone being after you, fear of losing a job and on and on.