Snowdon - approx 360,000 walkers a year. Very large potion of these are NOT experienced hill goers.
Llanberis Mountain Rescue - 200 callouts in 2016. Less than half for people injured, the others are lost or a bit scared.
So a 1 in 3,600 chance of an injury call out.
In terms of death and serious injury (for serious I mean life threatening or life changing), this drops to less that 10 in a year. So a 1 in 36,000 chance of death or serious injury on Snowdon. Bear in mind the profile of people who climb Snowdon too..... That's pretty low. You have about a 1:25,000 chance of dying on the road in Britain each year (of course you spend much more time driving that you do climbing Snowdon), but we're all pretty OK about taking that risk.
Learn to navigate, take sensible equipment you know how to use and if walking solo make plans so someone will soon miss you if you don't return. Consider a locator beacon of some sort.
But, don't have nightmares about it..... you're probably just as likely to die in the car on the drive to the hills. I'll close on that cheery thought!