Does sleeping for more than 14 hours frequently cause any damage to the brain? (ex. brain cells, neurological damage)?

Sleep is good: Sleep is good and necessary for the brain. However, in some conditions the brain may cause too much sleep. This may indicate that there is something wrong - often medication effects, infection, or toxic state. You should have a thorough medical evaluation. If okay, then your body just needs that much sleep. If you maximize the wake hours, that much sleep may be appropriate.