At what point does sleep deprivation become a problem?

I struggle with sleep deprivation as well. I noticed it became a real problem when it started to cause me to hallucinate in class. It started swinging my mood completely and it started to drive my psychotic. You should seek help as soon as you can for either medication, guidance on a better sleeping schedule, or to see if your sleeping problems are being caused by something else.

To the point where you sleep all throughout day and screw up your school/work schedule completely. Been there.

Sleep deprivation becomes a problem when it starts to negatively effect your mood, concentration, and/or ability to function throughout the day

One day is enough to affect mood negatively and rob you of a couple IQ points. About 6 hours a day serves as maintenance for me personally, and less than that means I'm stupid, irritable, and prone to depressive spirals. Of course, the specifics vary. I suppose the best way to tell for yourself is to keep a mood diary (or a log of anything you want to measure), fix your sleep schedule, and take note of the difference.

Sleep deprivation becomes a problem when you begin see it interfering with your daily schedule and functioning.

Sleep deprivation may seem minor at first, but can become very serious. The first signs that it is becoming a big issue include, excessive laziness, not feeling energized, and loss of motivation. It really becomes a problem when it affects the way you act, and interferes with your ability to complete daily activities.

When you can no longer concentrate then you're really in trouble. And when you start having hallucinations is when you need to see someone about it.

When it affects your day to day life. If you find yourself not being able to focus on things, or your sleep deprivation is severely affecting you - especially if you suffer from depression, sleep deprivation can make depression a lot worse.

The point where you feel emotionally and/or physically drained. When things you used to find fun in are now dull and all you want to do is sit down and do nothing.

When it effect relationships, concentration and fullfillment of life in general. It also becomes an issue when you feel dissatisfaction and it leads to other mood issues such as depression.