You must check that your site is available from outside of your network. You can use sites like http://www.downforeveryoneorjustme.com/ to check that your site is accessible. If it passes this test, then likely there is nothing for you to do.
I have seen issues such as this where a network is failing to resolve the domain name, or fails to deliver either the request or response packets. This can happen especially when there are routing problems but also when packet loss occurs.
The user can do a nslookup to resolve the domain name. As well, they can do a ping and check for packet loss. Ultimately, a tracert or traceroute can be used to see a proposed route. Trace routes are not always the route that a request is made so the results may not always be conclusive.
It may be that the user needs to contact the network provider or simply wait. I often remind people that TCP/IP is not a guaranteed delivery mechanism. It has built into it the option to fail. It is the client that must retry the connection and not the network. Browsers do not retry anything. They just fail. It is the user who must retry the connection. If there is consistent failure then there is a problem. Keep in mind that requests from a browser can fail for small reasons from time to time.
Also note if your users are from a particular geographical location, or network. This may help you to know what is going on.
Otherwise just give it some time and see if there is a change.