See Clear

Usually other people can tell you’ve been through some trials with one good look at your bloodshot eyes. They are unsightly, to say the least, but there are several things you can do about these lines, patches, and hues without going to the pharmacist. But it can’t be made clear enough that if you are experiencing pain in your eyes in addition to this redness, then you probably should seek a doctor.
Red eyes are primarily caused by dilating blood vessels that become much more visible when your eye is strained. More likely than not, if you are not experiencing pain from your eyes and the redness is the only symptom, just a good night’s sleep or eye-drops will do wonders. But eye-drops are not a cure-all for red eyes, and it’s even harmful to use eye drops regularly as they will cause the same dilation you are trying to cure. If you want purchase eye-drops, find ones that mimic your natural tears and ask a pharmacist to make sure they actually do that to sort out the marketing gimmicks.
Red eyes can also form with stress, irritation, and trauma. The gentle consistent irritation of contact lenses can cause red eyes. And larger more sudden trauma, like a good smack to the side of the head, can cause blood vessels to actually rupture and turn the whole eye red. You also could earn yourself something called a "subconjunctival hemorrhage" just from violent bouts of coughing or sneezing, causing a red patch to form on the eye that looks like many crisscrossing lines. However, these can arise from blood pressure problems as well and should diminish as you battle your other health issues.
Your eyes may redden from infection as well, but these are much more serious and you should see a doctor. Conjunctivitis, blepharitis, and other infections should be medically treated in order to ease your pain and prevent their spread. Also, make sure to not let your eyes touch anything others may use if you discover you have these conditions, like pillows or mascara.