It's very easy to fall into, but hard to come out of.
I'm not here to tell you to dismiss that feeling, but to try and understand it. A lot of the time we aren't even sure why we feel this way or we just don't care to go to the root of it all. So first you should try to accept this feeling. Too often people, especially my generation, hold things in and try to cover up how they feel and make it seem like nothing affects them. If you ever come across someone who always seems happy, trust me it's a well put together cover up. No one is always happy and to continue to act that way isn't wise. It's sad some even try to put others down for being "too emotional". We all need to realize we are HUMAN and as humans we are emotional beings. We need to let it out at least sometimes. So whatever feeling you feel towards something or someone know that it is natural and in no way wrong. It's only how you choose to react towards those feelings determine what happens next.
But first once you've accepted this feeling, ask yourself "why do I feel this way?" Be real with yourself because most likely whatever is making you uncomfortable to even think about, is the reason why. When realizing why, it is okay to let yourself to be sad or upset. If you cry, even better! Letting out all those suppressed feelings will help to make you feel lighter and easier for you to shake off all the negativity. Also, it is always a good idea to talk to someone who you trust with your feelings and someone you know would never judge you. If you aren't able to find someone to confide in, get some paper and a pen and write it all down. It doesn't have to flow, it doesn't have to make sense, it could even be a bunch of angry scribbles, whatever works for you. Whenever, I'm writing I like to write to soothing instrumentals. Here are two for you.
Now that you've went through acceptance and let out your frustrations the best you could, don't let the negative thoughts continue to fester in your mind. Write down a list of things you can do to help you get to where you want to be. For example, if you're not a fan of your current job think about what you really want to do and take steps towards it. Even if they're baby steps, as long as they're often something's gotta give! While you're taking your steps forward, in the meantime think about the little things that bring you joy. So you can keep yourself from getting into a depressed state.
Are you artsy? Grab a pen, pencil, marker, whatever and some paper and draw! Even try a medium that you've never tackled before but you've always wanted to work with. Whether it's painting or even crocheting. You could find out that you're really good at something all because you tried.
Feeling lonely? You can try to find someone to spend time with, but sometimes that doesn't work out. So have some "me time" whether that involves just taking a walk, treating yourself shopping or taking yourself out to eat. Small things like these can really make you feel good inside, plus you won't even have to worry about what someone else wants, it's all about you right now.
Now the last thing I ask of you, is to try to keep a positive mindset. I know it's not always easy, but positivity can really take you a long way. As bad as it may seem to be right now, you will be okay. Just continue to do the best you can.
"The light at the end of the tunnel is your life; It's the tunnel that's temporary."