How damaging is relegation to the third tier?

[Eric the Half a Bee]

Took us 20 years last time so I say it can be really damaging.
Portsmouth
Sunderland
Ipswich
They have been down there a few years now and Sheffield Wednesday are finding how hard it us this season
We need to stay up if we can and try and kick on and improve sensibly over the next 5 years.

It needs to be said that these are among the current worst case scenarios.

I would also add that there's absolutely no way this club would spend 18 years in the bottom 2 tiers as things stand.