hi film, this is another situation like the pain, headache, etc, where i would suspect magnesium problems. did you start taking some of your daily magnesium at a different time from the vit d3 yet? you may need to take a break from daily d3 and concentrate on magnesium for a while..
Dysphagia and Vertical Nystagmus in Magnesium Deficiency
http://www.annals.org/content/89/2/222.short
Downbeat Nystagmus With Magnesium Depletion
http://archneur.ama-assn.org/cgi/conten ... /38/10/650
Downbeat nystagmus indicates cerebellar or brain-stem lesions in vitamin B12 deficiency
http://www.springerlink.com/content/g5612882565x5388/
(btw, you need magnesium for proper absorption of b12 too, not just for greedy d3

)
random site because i'm out of time:
"Because deficiencies of vitamin B12 are most often caused by an abnormality in the absorption of vitamin B12, it’s recommended that supplements of vitamin B12 be taken with iron, folic acid, magnesium and vitamin B6 to facilitate its absorption and use by the body."
although magnesium is a really likelyl suspect to me, you may want to consider vitamin B1 (Thiamin) also:
http://journals.lww.com/greenjournal/Ab ... ble.4.aspx
Wernicke's Encephalopathy: A Predictable Complication of Hyperemesis Gravidarum
(ie you can end up with vit B1/ thiamin deficiency and nystagmus from other causes than alcohol)