Camera shake

For a simple way, try that. For something a little more heavy, might be a little to much if you just want the camera shake : ShakePosition de iTween.

You could use a sin function with a damping constant. (Sounds scientic!!!)

Ae^(-kt) cos(wt)

e^(-kt) means e to the power of (-kt). This function will creates a large oscillation depending on you A that will reduce in time to finish to 0. The duration and tilting of your camera depends on the (-kt).

That might not be what you want but if that can lead you somewhere.

You have to save the original position bud. There's no other way.

Your randomisation using the unit sphere is perfect: BUT you have to do "two jiggles" at a time. Always move it using your current system, and then in the new step simply return it to where it was.

Just use parity (i.e. odd/even) to know which you are supposed to do, ok

This blog covers it pretty well: http://unitytipsandtricks.blogspot.com/2013/05/camera-shake.html

For the record it is extremely hard to actually program the physics of hand-held camera shake, "wind" shake, tripod shudder, and other versions of camera shake. Note that in unity you can simply attach a spring to the camera and let physX do the work, no coding required. This would be a winning idea since, uh, you pay $4500 for Unity "since it has a physics engine". So use it. By no means does a "spring on a camera" produce really realistic "camera shake", but it's better than using Perlin Noise. Perlin Noise is sort of ok; the other "solutions" on here are silly.

Getting back to the actual question asked by the OP, conceptually yes you have to save the "original" position (indeed the "base" position, which in any non-trivial system will, of course, be moving. You have to have a whole complicated system representing where the camera is "ideally" and so on.)