Internet on the laptop suddenly extremely slow?

The Internet on my laptop has been extremely slow since yesterday. I drove the ICE yesterday and connected to the free Wi-Fi there. I could hardly do anything because everything was loading so slowly. I thought it was because of the Internet and I didn't think about anything else. I was at home today and the internet was still extremely slow. On the cell phone, tablet, etc., the internet is just as fast as always, just not on the laptop.

What could that be? I would appreciate an answer.

Virus? Have you already done a scan? Otherwise restart the Lapi or / and the W-Lan stick (if available) to another port?