What are mood swings?

It's a phenomenon of moments where one moment you are like ' Yeh duniya, yeh duniya pittal ki..yeh duniya pittal ki... baby doll m sone ki, baby doll m sone ki'
And the other moment you are like
'Yeh duniya...yeh mehfil...mere kaam like nahi..mere kaam ki nahi..'

Sorry if this wasn't relatable. I m so high on mood swings..ARGHH