@Kenshin
I'm not certain, I seem to remember it caused various things to rev up as it affected the nerves and straightened things out, as a side effect. My nerves had been been noticeably, excruciatingly, fried for several months before I was given it, so it made sense to me that it could do this (help the function of my nervous system in general not just the obviously painful bits), no idea if I'm right.
This "could" be what you were feeling. It did feel weird, and I did feel "ill" for a while, but I feel ill, and sick, all the time anyway so I just ignored it.
*edit - I'm not, I stress, advising you to ignore it, only you know whats out of range for your body, and what you're prepared to tolerate vs what feels like a problem.
I can't say I've noticed it taking a week to kick in, as far as I can tell, under normal conditions, it will completely run out in about 2 days if I don't take it, by the 3rd day I need it or the neuropathic pain builds rapidly. At this point if taken it will have some effect within an hour but takes 3 or 4 hours to have full effect, on me, but me and painkillers, or most drugs, is not normal.
However, full effect is rather limited, it's only partially effective, for me, on it's own, possibly coz the dosage is fairly low. As you say, takes the edge off.