I just wanted to update this thread so that it's got better information. I've been off the synthetics for 8 days now and I'm beginning to feel back to normal. The withdrawal symptoms have subsided almost entirely except for maybe a little restlessness or irritability. A little bit of depression kicked in a few days ago, but now that's gone too. So if anyone is curious about how long it takes to kick a synthetic THC/Spice habit, I'd say 8 to 10 days before you start feeling good again.
Synthetic THC is not an alternative to marijuana!!! Do not use it. It's a very dangerous and addictive chemical.