As you can tell from most of the replies above, this is NORMAL behavior of your body as you adjust to proper levels.
The body is used to something higher, and as such reacts with the shaking, weakness, etc., as you approach real normal levels.
Be patient and this will pass. Your body will become accustomed to what the levels are once you remain there, and it will function properly there. It just takes a little while. How long it takes to adjust can be from a couple days to a few weeks. But it WILL adjust.
Good luck!