The first place to check if you are having issues with your site is the Tsohost Status Centre page.
I started receiving a site down alert from Uptime Robot at 9:19 BST for this domain. First I checked the site and it was running very slow, the temptation is to raise a support ticket but its always worth checking the Tsohost status page. In this instance they had already logged an issue regarding a DDoS attack on their network. As you can see from the transcript below the attack subsided and then recurred again at 11:44, this coincided with further alerts from Uptime Robot which confirmed the accuracy of both systems.
DDoS Attack Against a Load Balancer on the Cloud
Logged: Monday 15th June, 2015 @ 09:05 | Last Updated: Monday 15th June, 2015 @ 11:56
Summary: Our Network Engineers currently investigating a DDoS against the load balancer at 95.142.152.194. This may cause slow loading for some websites. Please bear with us whilst we work to bring affected sites back online.
Affecting: Cloud Hosting
Updated: Monday 15th June, 2015 @ 09:22
Our team are still mitigate the DDoS, and we currently do not have an Estimated Time of Return for affected sites. We apologise for the disruption this morning morning’s downtime and for the inconvenience caused.
Updated: Monday 15th June, 2015 @ 09:40
The DDoS is currently under control, and we are closely monitoring our service to ensure it does not resume.
Updated: Monday 15th June, 2015 @ 11:44
Unfortunately the DDoS has reoccurred, and we are again working to mitigate this attack. We hope to have affected sites back online in the next 5 minutes.
Updated: Monday 15th June, 2015 @ 11:56
Sites are again back online and the DDoS has been mitigated, however we are continuing to closely monitor the situation in case of repeats of this issue.