I am sorry you are struggling. It certainly sounds like you are depressed. I have just come out of a manic episode and feel the depression sneaking in. It is a common thing for depression to follow mania. How long does it usually last for you and what have you done in the past to manage your depression? Is there an on-call pdoc you can contact while yours is away? If you can't see a doctor but are safe it is best to use skills you know, or learn new ones, that help manage the depression in a practical way. Like trying to do things that interest, or used to interest, you, eating well, sleeping on a routine, socialising and trying to get out of the house more.

Try to fight the depression with all you have and it will at least make a dent in your suffering and get you through till you can get your meds changed. It does sound like a med change is needed. For me Lithium does nothing for depression and I haven't used Seroquel a lot but when I did I was still depressed. Take care and take each day at a time.