I found one site...that said "may"...

http://www.evitamins.com/healthnotes...tentID=1538006

http://www.ncbi.nlm.nih.gov/pubmed/3189539

Vit D has many uses in the body besides calcium absorption and transport.

when it is low, it is prioritized to the bone calicum issues.

This site is very inclusive for Verapamil:
http://www.umm.edu/altmed/drugs/verapamil-131700.htm

I don't think there is a fixed proven answer to your question at this time.
Your use is not involving heart/blood vessel issues, where most of the
research focuses.

What I see Vit D doing is improving calcium absorption in the GI tract.
Much of the supplement forms of calcium are NOT absorbed (about 20-25% only) Vit D does not affect polarization of calcium channels.
When you are low in the diet for calcium the body will rob your bones for it.
The use of the Vit D in proper amounts is to avoid this robbery.

The vitamin D research is focusing on testing and getting people to be in normal range for it. We are not talking mega dosing or extra calcium supplementation.

I then searched the verapamil/mania keyword in PubMed:
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum
this was the only one I found that suggested this use is not
effective for many.
The other papers show mixed results.

Until the exact mechanism of calcium disruption in mania is discovered, I don't think there is an answer to the question that is reliable.

I'd get the blood test, to see where you are.

This paper was interesting...shows magnesium improves verapamil response in mania. It just might be the key to improving mania in general! (it improves migraine as well, which is also thought to have a "seizure like" trigger). Magnesium also antagonizes the NMDA receptors for
calcium -- calcium triggering pain, and magnesium blocking it.
http://www.ncbi.nlm.nih.gov/pubmed/1...ubmed_RVDocSum