Why the pain from sciatica is terrible in the morning and how the day passes is less severe,is that normal?

Disc Hydration: Disc are more fuller in the AM after a nights rest due to the absorption of fluid overnight. Thus fuller discs can herniate more and cause pain in the AM, then as the discs lose fluid throughout day they do not compress the nerves as much. Also the reason the AM is the worse is because the discs do not irritate the nerves all night while sleeping and start irritating upon waking.