Sleeping with contact lenses is not really dangerous enough, but it indeed has a side effect on your eyes. Depending on the type on contact lenses you are wearing, there can be varying effects of sleeping with contacts. If you use daily contact r lenses, then you may wake up with really dry eyes. You may find it really painful to blink till you splash some water in your eyes, and also experience some soreness, irritation, puffiness and redness in your eyes, the lenses become dry and your eyes are irritated, so you wake up with uncomfortable eyes and your lenses may tend to irritate you more throughout the day, especially later the next evening when it is time to take them out. On the other hand, if you are sleeping with extended use contact lenses, then you are quite safe. Depending upon the type of extended wear lenses that you are using, the effects may vary.