The "losing momentum" thing gets overstated sometimes. I work in healthcare and I've trained with people who took gap years and came back stronger, and others who never lost a beat going straight through. The difference wasn't about the year itself - it was whether they had a concrete reason to defer. If you're deferring because you want to work, travel, or genuinely figure out if this program is what you want, that's solid. If it's vague anxiety or you're just not feeling it yet, that usually doesn't get better with more time sitting around.
What concerns me more is the "not ready" piece. Not ready how? Are we talking about academic prep, mental health stuff, financial reasons, or just cold feet about the commitment? Those need different solutions. Cold feet about a major life decision is actually pretty normal right before it happens - I see it with patients before big surgeries all the time, and most people who push through are fine. But if you're genuinely burned out from high school, dealing with depression, or unsure whether this field is actually for you, then yeah, taking a structured gap year with a purpose makes sense. Just sitting around waiting to feel ready probably won't get you there.
The momentum loss comment has some truth, but it's not automatic. If you defer, you need to *do something* - internships, work experience in your field, volunteering, whatever makes sense for your program. That keeps you connected and actually strengthens your application if you ever need to reapply elsewhere. Going in September out of obligation when you're genuinely unprepared is the real risk. You might struggle, burn out, and then actually lose years.