Very long time to first byte

Hi
On one page, I repeatedly have a very long time to first byte. If you look at http://www.webpagetest.org/result/120105_W6_2RH59/,
First view: 85.5 secs (first byte: 76.3 secs)
Second view: 9.9 secs
Third view: 4.2 secs.

The home page shows a similar story (http://www.webpagetest.org/result/120105_50_2RH84/):
1st: 52.2 secs
2nd: 4.5 secs
3rd: 5.6 secs

The site is Joomla with a JAT3 template which minifies, combines and caches files. This slowdown is recent and I just can’t pinpoint what might have caused it.

Any idea what might be causing this?

Thanks
Carl

Holy cow, reach out to your hosting provider and have them take a look at the web server and (more likely) the database. My best guess is that the database fell over and is running really slowly.

Do you know if your back-end makes any calls out to any other services (spam validation, IP location or anything like that)? If so then it could also be a 3rd-party back-end that is having problems.