Raphael Natividad is guilty of something most millennials don't usually do: ignoring his phone.

Natividad, who recently graduated from the University of California, Irvine, with a degree in heath policy, has a legitimate reason, one that speaks to an existential crisis that has befallen a growing number recent graduates.

"I was ashamed that I didn't have a full-time job right after college, and that shame made me hesitant to spend time with underclassmen or with peers who I thought had brighter futures," Natividad told CNBC in a recent interview.

"I consistently tried to avoid people, and I would ignore messages on my phone or on group chats to avoid any conversation about the future."

Although not an official designation by the American Psychiatric Association, a few therapists are using the term "post-graduation depression." According to mental health professionals — and recent graduates feeling its effects — the condition is characterized by a period of severe sadness, loss of motivation, helplessness and isolation due to constant change and an overabundance of choices.

From kindergarten through college, school becomes the primary structure giving students a sense of certainty, while providing them with a social network for learning and support.

Yet after graduation, that structure crumbles, and with no set timetables or mandatory classes to study for, anxiety, depression and a sense of loss about what to do next become all too common.

"This is a real issue unique to this generation called 'a quarter-life crisis,'" said Cyrus Williams, a licensed professional counselor and an associate professor at Regent University in Virginia. Millennials are "struggling in terms of milestones, getting jobs, parenting, finding jobs, having too many choices, and having debt coming right out of college."