What are the negative effects of meditation?

What studies or theories compare the effects of meditation and sleep?

• More specifically, does meditation provide similar organizational benefits for memory and emotional regulation, as are being hypothesized for sleep? In practical terms, what would be more restful when one is tired, a half hour of sleep or (some kind of) meditation? Reference http://www.frontiersin.org/Journal/10.3389/fpsyg.2013.00474/full

• Answer:

  The notable scientific difference between meditation and sleep are the different type of brain waves generated. Sleep is categorized by four levels of depth, the deepest of which can produce up to 50% delta wave activity, stimulating the production of hormones like melatonin and dhea that eliminate free radicals and repair damaged cells. Delta waves are the lowest frequency brain wave and are characterized by deep sleep and the regeneration of the body. Meditation is a wakeful relaxation, and although skilled practitioners can produce delta waves in medtitation, most people who meditate go only as low as theta waves and alpha waves (or in some types of meditation one may increase the frequency of his or her brain waves all the way up to gamma waves).   http://www.sleepwriter.com/2011/11/can-meditation-replace-sleep.html Is a good link about a study where tests were done to show wether meditation or sleep is best for rest. It basically states that one or the other may be better in certain circumstances