I ALWAYS STAY UP LATE AND SLEEP IN LATE - UNHEALTHY?

I am going to college starting late Aug but during the summer, I always stay up extremely late and sleep in really late. Like I will stay up till around 3-5 in the morning and wake up around 2-5 in the afternoon. I've heard this is unhealthy and can be be damaging to my health. Is that true? How so exactly? I'm just wondering b/c even though it messes up my ciracdien rhythm, it's not sleep deprivation b/c I'm still getting a lot of sleep. Plz help, thx! 10 PTS!