Your reflexes are affected by the alcohol, which absinthe contains a high percentage of.
There is no evidence that the wormwood in absinthe adds anything to the effects of the alcohol. It may be that absinthe got its reputation in the C19 because the drink was adulterated with other ingredients then, which did produce odd effects. It was once thought that thujone, present in wormwood, was the active ingredient but tests have shown that the drinker would have to drink more than the fatal dose of alcohol before thujone could have any effect, hallucinatory or not, on them. [ Source :wiki 'Absinthe']
Must say, I've had experiences akin to hallucination, just from drinking large amounts of alcoholic drink which was not absinthe!