Voltage between breaker box and earth
Well, there’s only one source of power there, so if you got shocked at all, it was by 120V.
You still live because the resistances of the available current paths are wildly variable due to all sorts of factors including meteorology.  So you got lucky today.  Don’t try to get lucky tomorrow; that is to say, don’t count on that high impedance repeating itself.
It sounds like your electrical panel’s Grounding Electrode System relied on a metal water pipe which was improperly changed to plastic without addressing bonding.   There might also be other problems with the grounding system or the Neutral-Ground equipotential bond (the connection between N and G in your main panel).
Yes, as George describes, that wire going back to the service pole is neutral, not ground.  They are not the same thing.  The power company does not supply ground, but they do tie neutral to ground at the pole transformer.  This means there are some fault conditions where power will try to return via the earth to that transformer-pole ground.  Dirt is an exceedingly poor conductor, so this doesn’t flow a whole lot of current; and since it doesn’t, it creates a voltage gradient along the route.  You may have encountered some of that.
Some of your house’s appliances may have a ground fault, but this is not the time to address that; now you want to go over your Grounding Electrode System and your Neutral-Ground equipotential bond with a fine tooth comb to make sure all is in order.
Next, I’d use that voltmeter to make a perfunctory check of all the receptacles in your house (or rather, one per circuit, or rather, one per leg of service if you know what that is.  We are looking for voltages that are not 120V, but which add up to 240V-ish.   So if one leg is 99V and the other leg is 142V, that’s the red-flag.  Further this will change several volts if you turn on a big 120V appliance like a hair dryer or toaster.  This would indicate a lost neutral, which means your house is trying to return all imbalance (neutral) current via the Grounding Electrode System. That is easy to fix and it’s almost always in your power company’s bailiwick, so it’s free to you.