Thank you for your interesting question.

There is an opinion that the upper daily intake of Vitamin C should be limited to 2000mg. although we should point out that such is the diversity of views that one source quotes 60mg as the recommended daily intake. Either way, it is clear that you are exceeding the recommendations by an excessive amount and it would be unwise and irresponsible of us not to advise you to make a drastic cut back on your intake, if for no other reason than it may lead to unexpected and unwelcome consequences.

However it is also important that you only gradually decrease your intake to a more reasonable level, and not attempt to get back to a normal level overnight, so to speak. If you cut back both dramatically and immediately you stand a chance of “rebound scurvy”, an unpleasant and possibly fatal condition, for reasons that it is not appropriate to explain here.

The human body does not produce vitamin C, it is absorbed from the food we eat. In normal circumstances excess vitamin C (a.k.a. absorbic acid) is excreted in the urine and is unlikely to be harmful. A significant excess may cause one or more of the following symptoms : Diarrhea, vomiting, headache, insomnia, kidney stones, increased urination, osteoporosis, joint pains and heartburn.

Your feeling of being euphoric or “high” may be due to the vitamin’s function in neural transmitters and /or a high concentration being stored in the adrenal gland. Although we do not know of any connection, and must be taken solely as our guess, it could be that the constant excess of vitamin C may trigger a release of adrenalin from the gland or stimulate your neural transmitters to give you that “high” rush.

As with any extreme excess to do with the body, our strong advice is gradually reduce your vitamin C intake to normal levels as you cannot be sure of the long term damage you may be causing yourself. As they say, you should take “everything in moderation”.
We hope this helps.