Rapid mood swings are something many can relate to. While they are common, they aren't pleasant experiences for us and the people around us. I believe, they can affect our relationships a lot. To handle that, I try a whole lot of things like writing journals, distracting myself, painting, drawing, reading, etc.
Maintaining journals is an excellent way of keeping a track on your mood swings. Especially when you have trust issues. Talking to someone might help, in the alternate case. Try to go deep into why you are feeling what you are feeling, what makes you feel like that, what are you actually feeling, what do you think the emotion might be, what upsets you, what, according to you, is the reason behind the mood, etc. Try asking a lots of similar questions to yourself and try to answer them in the form of journals, enteries or as a self interview. After the episode, when you reflect back on it, you will com across many things you weren't aware of, about you.
Distracting helps a lot if you don't want to talk/think about it. Try grounding techniques, colouring ready made pictures, painting or drawing pictures. You may try reading, listening to music if you aren't a big fan of drawing. Anything that distracts your brain is good enough.
You may also try to think of a pleasant experience/moment or someone you are grateful to have in your life. Try to word out a memory where you feel cherished, loved or describe a person you feel blessed to have.
If nothing works, you may also try to describe a situation/place/person in as much details as you can.