Ok so before i get on with my theory i would like to say two things, One: I have this on my main page but i wanna go ahead and put it on the main blog Two: I have no idea if this actually happens so read at your own risk of a !!!!!!!!!!!!!SPOILER!!!!!!!!!!!!!!! With out further of due may i present ...............
What Dr.Brenner ment by "sick"01:34, September 24, 2020 (UTC)~
Ok so if you think about it before El left the lad she never got tiered or past out she just used her powers with out getting tiered or passing out. After killing Dr.Brenners people El passed out and didnt wake up for awhile and Mike knew somthing was wrong, and then Dr.Brenner grabed El and told her that she was "sick" and he tells her that hes gonna take her back home to the lab and make her better.
What if El's source of power is the Mindflayer? What if in before season one and she was working with the mindflayer but she didnt really understand it until Mike. What if she is basiclly useing her powers againt her self. if you think about it even more her powers come from the mindflayer,but now after season 1 she is againt the mindflayer sp its hurting her and Khali  in season two makes an illusion of Dr.Brenner saying that her powers will eventually be the death of her, at the end Khali says that they [ Mike and the rest of the gang ] cant save her El says i know but i can save them.
01:34, September 24, 2020 (UTC)~ i have more theories to come, please comment and let me know what you think [ please ask permision before reposting any of my theories, not that there even good enough for that ] also this is all my opinion and THANK YOU!!!!
~ your fellow Stranger things fan