Mail has suffered recently from a couple of individual and intermittent performance difficulties. The service status checker was showing this as a national issue. Bet that is what you have been experiencing. Should all be clear now. In case this has affected the way your Chrome browser works clear your browser cache and cookies. That should sort it.
I use Chrome and it performs well.
Superuser 2017/18 Use Kudos to say thanks Mark answer as "helpful" only when the problem is solved Please don't send me private messages unless I ask you to. I do not work for VM. The advice I give is based on my best understanding of VM policy and practice. You rely on it at your own risk.
Have you measured the speed of your connection recently?
Run www.speedtest.net periodically to check what speed of connection you are actually getting, as opposed to your nominal speed, and also observe from the graph produced whether your signal fluctuates up and down or is relatively steady. I don’t suppose you will know whether VM has added a dozen new customers to the green box in your street to which you are probably connected. You are all sharing the total capacity of the box.
Note that “no changes to my system” is a false assumption. Most websites you visit will add a cookie or 2 to your browser’s store of cookies. And the upper limit is around 3000 of these.That’s why Howard has advised you to clear them out periodically. Multiple cookies for the same site over a prolonged period of time can cause confusion between your browser and the website.