On a ride the other day my rear shifter starter acting funny in a way that when I tried to shift it required a little more effort to shift and the click response was alot louder. Then all of a sudden towards the end it started acting normal. Is this something I should be concerned about maybe shifter going bad? Maybe just needs lubed if so how? Has anyone else experienced this behavior before?

my guess- cable friction. specifically, bb cable guide friction. its all sticky. you ride, you drink some water or drink, some drips down to the guide, gets it wet and slippery. you finish, any sugary drink dries up to glue, making shift effort higher until the next time it gets wet.
entirely speculation, of course.