Fully charged iPhone 12 thinks its dying then shuts down?

Recently, I shut down my iPhone and turned it back on. However, now when I use it, I am only able to do things on it for maybe about 5 minutes. Afterwards, its starts getting extremely laggy, says it has 1% for only 2 seconds, then switches back to 100%. After that, it goes to a black screen with a spinny logo, but the spinny logo isnt moving. Then it completely shuts down and I have to wait a full minute before it starts rebooting again. Whats going on with it? I've never seen this issue before.