I think if I personally did it more than once a week I would probably become psychologically addicted to it, and would start doing in more and more untill it became a daily habit, and that IS BAD! But if you don't have an addictive personality, I'd say you'd be safe to do it again one more time this week, but you might have a slight tolerance since you only did it 4 days ago. It becomes a problem when you start using it once a week, every single week or more. I try to keep it no more than once a month, but I'm out of weed myself... it's only been about 2 weeks for me, but I think I'm going to end up doing it next week (which would make it 3 weeks instead of a month). But after that I'm going to have such a huge supply of other drugs that I probably won't do DXM for months after that. Basically, you can do it two weeks in a row if you plan on having a 2 month break after. Any more trips than that and, again, you probably won't stop there and eventually fuck up your head and other bodily organs.

I'm not a huge expert, though, I'm just speaking from the experience that I stay healthy keeping it monthly or longer, or occasionally two times a month if I haven't done it in a while.