I have an actual minor deficiency as well and had accidentally bought the wrong potency (the bottles are identical except for the 4 pt flyspeck font specifying the amount) from the store and had been mistakenly taking 5000IU/daily instead of 1000IU/daily for about 6 months. When I informed my doctor of my mistake, he ordered a test and although my serum vitamin D levels were not outrageously high they were at the upper limit.

So definitely easy to "overdose" on vitamin D and as you point out - the potential side effects are not pleasant.