I have severe anxiety, but why am I almost constantly full of jealousy or anger towards others?
First of all, having these moments of jealousy or frustration when you see others around you succeeding in areas that you would like to is completely normal. We all have those thoughts and because you are in your head and know your thoughts, it is easy to get very self-critical.
Making the efforts to rejoice with your friends and be happy for them is good but I do think it is important to know this does take effort and is not always our first reaction. Especially since you are struggling with self-worth, you might find yourself comparing yourself to others and feeling threatened when you do not feel you are measuring up. However, we are often too hard on ourselves and need to exercise grace. Growing up, we are often told the Golden Rule of "Do unto others as you would have them do unto you." I like to take that and reverse it and say "Do unto yourself as you would do unto others." Often we are so self-critical and tear ourselves down when we would never do that to another individual. Would you look at a friend and tell them that they are "dumb" or "a loser"? If we would never say those things toward another person, why is it ok to say those things to ourselves? It's not. We have to try to challenge and redirect the way we talk to ourselves.
As far as some tips for dealing with anxiety and getting out of your head -- Mindfulness techniques are helpful when dealing with overwhelming and intrusive thoughts. A great one is where you try to utilize all of your senses in order to ground you to your surroundings. It basically is counting 54321: What are 5 things that you can see? 4 things you can touch? 3 things you can hear? 2 things you can smell? 1 thing you can taste?
Another technique is mindful breathing where you will try to focus on your breathing and push out any thoughts. When thoughts come you can acknowledge them and try to move your thoughts back to focusing on your breath.
Also with anxiety, it is helpful for us to recognize our physiological response to it as this helps us to have a clue on how to calm our body. If you are feeling tense, try to relax. If you are breathing heavy or fast, try to slow your breathing (taking a sip of water helps this a lot actually). By calming our body's response to anxiety it can actually reduce our anxiety.
Finally, acceptance helps to play a big part in reduction of anxiety. A lot of our worries about about things that are out of our control or unknown to us now. Trying to accept that there are things in our life that we cannot control and recognizing that it is what it is can help with reducing our anxiety and need to control certain things in our life that are beyond our control.