One of the most important things I ever learned about managing mental health and emotional distress is that emotions are a physical thing happening in your body, and that more often physical things happening in your body are the cause of your emotions rather than anything abstractly mental.
Yesterday, due to whatever poor decisions I was making, I had 310mg of caffeine, half of that after 5pm. Predictably, I had trouble sleeping and spent all night jittery. Today, I feel exhausted, jittery, and overall awful.
It's very easy, at times like this, to feel emotionally awful about a lot of things in my life that are far more abstract than "I slept poorly." I might find myself questioning who I am, or my life choices. I might feel unsure of what I really want, and things I felt very good about two days ago now might feel alien and unsatisfying.
I might feel nervous, apprehensive, anxious, like I'm struggling to get through a rather quiet and banal work day, and interpret that as being about my job. I might feel crummy while talking to a loved one, and conclude I've fallen out of my feelings.
Tonight, I will go to sleep, hopefully sleep better, and wake up hopefully feeling better, and all those things may look much sunnier than they did today.
People talk about "never believing anything about your life after 9pm" and that's the same phenomenon. It's easy to interpret physical sensations as emotions about the state of your entire life, and not the state of being tired and sleepy right now.
"Hangry" is the same thing. It's easy to misinterpret being hungry as being angry about the world.
Learning to be mindful and attentive of your body, while describing it neutrally, can disperse this effect. When I first learned about it, I was 19, and I remember feeling palpitations and my heart racing and just full of anxiety and panic... and I just said to myself "Oh, my heart is just beating quickly right now. That's all that's happening" and didn't think at all about social interactions or anything important.... and the anxiety just sort of dissipated slowly as I sat and rested doing nothing.