applied for a job which is not my career progression - move sideways... feel a bit bad

[startnow]

feel bed in my ambition - but need a fresh start/environment to build up energy for the next post. or part of me thinking why not to be patient and wait for a better post and decline an offer that I have now?

I don't really understand your post. If you can get a better job simply by waiting it out in your current position (as you seem to suggest), why take a new position which is a move sideways? How will that help - apart from helping you to "build up energy"? What is it that you need from this move sideways which will specifically help with a promotion?

Plenty of people where I work have taken sideways moves to gain other experience or try something new. Not that many have taken a traditional career path that goes step by step up a single ladder. And it's not like you're committing yourself forever - this is merely the next step.