Sorry, I know this is an old post, in reference to your post, there has been a well documented link between choline and depressed mood.
Eggs are unfortunately, one of the highest sources of dietary choline, as are many other animal based and animal derived products. Some legumes also contain high amounts of choline too, but to a lesser extent.
Choline is an essential nutrient, but unfortunately an over abundance of dietary choline can effect mood stability, just as a deficiency in choline has also been linked to memory/mood problems.
The yolk contains the highest amount of choline, and the egg whites contain only a fraction.
There has been some anecdotal online reports from individuals who can continue consuming
hole eggs in their diet, if they supplement with inositol. It seems to balance or negate the mood depressing effects of choline.
Here is a reference and source of information that may elucidate further on the choline and depression theory: