Separation Anxiety: When Saying Goodbye is Hard — Deborah McNamara, PhD
This is a wonderful description of separation anxiety, with good tips on how to handle it at your house.
"Separation is provocative for young children because it is connected to their greatest need – attachment. The more immature one is, the greater the longing for contact and closeness because of dependency needs. They desperately need their relationships to work for them because this ensures they will be taken care of. Separation means facing the absence of their attachments and the more dependent they are on them, the more anxiety they can experience as a result. It is their desire for contact and closeness that makes them miss us when we are gone. Attachment is the doorway through which separation anxiety opens up."
Deborah McNamara's site is wonderful, check it out.