I've been on Lexapro (escitalopram) 30mg for the past six months and I forgot to take it today and will be out of town until thursday! What should I do?

Missed doses. Since you achieved a therapeutic dose some times ago (usually after 4-6 weeks) missing a couple doses should not bring on a sudden return of symptoms. Just remember to take your med when you return home. Lexapro (escitalopram) & other antidepressants stay in the system for at least a couple weeks after stopping them.