Hello, I seem to have run into a major problem. After flashing TWRP and flashing the Xiaomi EU rom for my phone, I out of stupidity changed slots when rebooting. I think I was in slot A, changed to slot B, rebooted and now I can't access my internal storage, it is marked with 0 mb available and I have no system either now. Do I have to download and flash the stock rom and restart from the beginning? Also, what exactly are those slots for? I was curious to see what they did, and my curiosity got the best of me. 
Thanks for any given answer.
Thanks for any given answer.