a) you're lying
b) you're VERY unlucky (since few places genuinely seal you in
c) Most likely, you didn't realise you were not, in fact, sealed in.

But ultimately, you must have set out without a potion to begin with.

On eastern, there are hidden exits.

In Keep of the Righteous, there's a hidden exit.

Anywhere else... why aren't you carrying a potion again? It's like you got cursed by a necromancer and then complain that you couldn't successfully go and buy yourself a teleport potion.