I think you are getting a lot of sleep and your eyes are irritated and puffy from oversleeping. These black lines or circles are probably prominent blood vessels which become more noticeable.
You should also buy Eyecon by BENEFIT. Its very useful and also try drinking a lot of water.
I have heard that cold used wet teabags and cucumber slices under the eyes can work. But lately I have heard of people using haemorrhoid cream (piles) can reduce wrinkles. If you don't know what it is just ask your mammy or your granny.:)
If you want to be all about nature ; try natural remedies, of course - by using tea-bags & hot water, or a cold spoon. Or icecubes work more efficiently, but they can be painful & uncomfortable] Warm some water in a cup, but don't make it too hot. Dunk the tea bag in the warm water, and let it soak it up for a bit. Take the tea bag out & place it on your eyes - laying down. Leave it there for 10-15+ minutes. It probably wont be dramatic, but it will do some justice. Same with the cold spoon, [if you really want, you can put it in the fridge for a while], put the cold spoons under your eyes, where the undereye-bags are & hold it there for 10-15+ minutes, or until they become warm. This should help. FOR A NON-natural remedy, you can try a good old concealer stick. Try to get three shades lighter then your skin, but don't go too light - because it will only further emphasize your bags. When testing, too - make sure you test it in natural sunlight. Because, most of the time, the stores light wont reflect the foundation as it would in natural light.
I have used lukewarm tea bags on mine and it works wonders try it!
My mums gets a that a lot and she's in her 30's. I would recommend ANEW avon uplift eyepen. It can get rid of bags and wrinkles under the eyes and also makes the eyes feel and look younger.
honestly I have this horrible lines under my eyes, but I learn this little trick that applies to people who have bags in their eyes or dark/blue/purple/blue lines or bags under their eyes. When you are done using your cream in your eyes and before applying make. Get orange lipstick, apply around your eyes, make sure to apply under your eyes, not to closed to your eyes, where you see that dark color or that bag. After applying this lipstick ( make sure is orange because orange kills blue) apply your regular make up or make to correct your eyes. Make sure you take your time to do this because if you apply it right it will help a lot and cover your bags or darkness. I know it sounds weird but I have seem that different big time. For a line under your eyes it won't work ... Trust me I have tried and I doesn't work.
Black lines or dark circles? If it's the latter, I have discovered this stuff called Ooh La Lift by Benefit that I put on before my concealer. It kind of has a lightening thing in it, so that your concealer doesn't make your eyes look darker. If you're talking about actual lines, maybe you forgot to take off all your eyeliner or mascara from last night! : )
Makeup and skin cream should work. There a special one for removing bags
I have severe black lines under my eyes what medication erases them all of the way.
I use primer (Urban Decay) and then cover it with concealer (Sephora) and blend it in with my skin.