Someone in a coma is not "asleep" they are unconscious. They don't respond appropriately to sensory stimuli, that is part of how they are diagnosed as being in a coma in the first place. So, the answer is no.
Yes there has been some sucess with Coma Arousal Therapy. It depends on the degree of brain function based some what on the Glasgow Coma Scale or the Rancho Level.You can read more about it at http://www.birf.info/home/library/coma/coma_excoma.html
"The startle reflex is the lowest level of auditory functionÂ*22 and as with visual stimulation, the type of response is dependent on the intensity of the stimulus. Noises that might cause conscious people to startle will not stimulate the comatosed. Therefore very loud noises (such as banging two saucepans together, ringing a bell or blowing a loud whistle directly near the patient) are needed to achieve a response. This noise stimulus should be irregular as the brain has the ability to "turn-off" continual sound.
The third sensory modality, touch, can be achieved by deep pressure massage, pinching and slapping, and use of a vibrator, loofah sponge and brushes is also suggested.Â*23 Whatever type of tactile stimulus is used it is important that it be "rough" as the intensity of the stimulus is the important factor in gaining a response.
Facial grimacing is an indicator that the taste sense is working and like other sensory modalities the intensity of the stimulus is important. HunterÂ*24 suggests the use of such substances as vinegar, lemon juice, mustard, soy sauce, chilli and salt as an intensive or noxious stimuli. Caution should be employed if the patient has an endotracheal or tracheostomy tube in situ. Smell may be stimulated with the use of peppermint oil, eucalyptus oil, garlic, strong perfumes, rubbing alcohol and spirits of ammonia.Â*25 Stimulus has been achieved if the patient grimaces or attempts to withdraw."