Welcome to clinical depression, or "Major Depressive Disorder"!
What is it? It's quite simple, it's basically death. You simply live like a robot or any other animal (eat, sleep, repeat). You were probably frequently exposed to negative emotions, so as a defense mechanism, your brain shut down some connections.
The brain had good intentions. It just wanted to remove the bad emotions that were there for too long... but it had to shut down the good ones as well! So instead of having fluctuating emotions, you have NONE. Zero, nada, nicht!
Like I said earlier, negative emotions makes it hard for humans to reach their primal goals such as find food, shelter, protect kids, etc. So the brain just permanently turns off all the connections related to emotions.
No more fun with friends and family, no more hobbies, no more desires, no more dreams, no more motivation... for anything!
If someone came to me, and offered me the choice between going to prison for a year or going in an all-inclusive hotel in Mexico, I would tell him my favorite response: "whatever" or "I don't have a preference".
That's what it feels like. Everything is neutral. I don't feel sad, I am just bored because my mind isn't producing feel-good hormones like serotonin. I have motivation for NOTHING.
The worst of all is that you can't do shit about it. Here's why...
You can either seek treatment, which doesn't work in most cases, and if it does work, you'll depend on pills like an heroin addict depends on opiates. Not to mention the side effects of most pills, such as loss of libido, a loss of appetite, a loss of hair, a loss of muscle mass, reduced bone density, increased fat gain, insomnia, etc.
Or, let's say you miraculously get cured one day... and you start having emotions again... can you guess what will happen?
You'll come to the realization that life is actually good and that you just LOST 2, 3 , 4, 5, or more years DOING NOTHING. That's gonna hit you like a ten ton truck.