Is anyone familiar how internet works in large apartment complexes? I went from having 100+mbps download and upload speeds to occasional under 10mbps.

Pretty much all connections (xbox, printers, etc.) are through ethernet. My computer uses wifi through a Nighthawk router. Just recently, it sometimes goes to a crawl. Like 2mbps download speeds for no apparent reason. Do I share a connection with my building through one modem or what?