The first thing you should do is gather proper information about the attack, whether DDOS or otherwise. While it is possible that you are the target of this attack, it is equally likely that your own system is the origin of these attacks - especially if you are running any mass-distribution CMS system. (You did say you use DirectAdmin...)
You can record about a day's worth of traffic with something like this:
tcpdump -w file -G 60 -W 1440 -s0 -p -C 5
That should tell you whether you need to write your own automated harakiri script. Understandably, since it is a rather desperate measure, you won't find one.
If you are the source of the DDOS, then, well, you can't expect much sympathy from your host - find out what is running on your system and kill it.
If you are the target of the DDOS, then you may be able to respond (or not respond) appropriately in a way that stops the flow of traffic. If you are already not responding, then the only thing you can do is hide away in your shell ... you could try this if you think your adversary will go away in 10 minutes:
screen # don't stay dead on shell hang-up
/etc/init.d/networking stop; sleep 600 ; /etc/init.d/networking start
If you have multiple IP addresses, then taking down just the targeted IP address should do the trick.
Your provider may be able to do something about tracing the source of the attacks, but don't hold your breath.