Link to original: http://sphynxcatvp.nocturna.org/articles/sangi-traits.html
Being naturally nocturnal, having excellent night vision, and/or sensitivity to bright lights/sunlight. Sunlight feels like a heat lamp radiating uncomfortably on your skin; you may burn easily, but not tan readily. UV lights -- a/k/a"black lights" -- drive you nuts to look at them.
Blood craving / bloodlust, (apart from any sexual or erotic draw towards blood), where you cannot get it out of your mind. Ingesting it provides you with a sense of peace, relief, euphoria, relaxation and invigoration. You crave the taste of it -- it tastes absolutely divine to you, you love the smell of it; you have a driving need to obtain and consume it. You have a chronic, insatiable thirst. You become weak, irritable, and feel out of sorts if you do not consume it fairly regularly; generally, you require it in quantities greater than "a few drops" in order to satisfy you.
Somewhat heightened physical senses, such as acute sense of hearing, smell, or touch; sensory extremes are uncomfortable or not easily tolerated. You can hear high-pitched sounds, such as the whine from a TV set or ATM machine that other people can't hear, or have difficulty hearing. Alcohol and other drugs affect you easily at lower quantities than other people; on the other hand, some report that they have an increased tolerance for alcohol and other substances.
A dual-personality (not to be confused with schizophrenia or Disassociative Disorder -- you're still "you" in mind, just not in your thinking or behavior......), a.k.a. "the Beast", which you have difficulty controlling when it surfaces. Generally it will emerge when you are in acute need for blood, if you become angered, frustrated, or your inhibitions are lowered due to distraction, alcohol or drugs. You experience emotions of any kind intensely and passionately; people remark that you can be melodramatic at times, though to you, it's just a normal expressing of your emotions.
Apparently, many vampires have increased psychic abilities and/or sensitivities, clairvoyance, etc.; this is not true for all. -- I, myself, have virtually none that I am aware of or put much stock in. Also, increased empathy (sometimes extreme empathy, where they have trouble telling whether what they are feeling is their own emotions or someone else's). Psychic vampires, or psi-vampires, draw energy from others, and will become perky, animated, invigorated, possibly hyperactive, while the one they are drawing from will become tired, weaker, or lackadaisical, disinterested. Many have an increased ability to manipulate energy.
Often, those who are real vampires were/are drawn to the vampire, or the vampire mythos and image, from a young age, often reading or watching and finding that they related to or sympathized with them; they have always had an inexplicable interest in vampires. Sometimes they are drawn to dress or act "like a vampire does" in order to express themselves or to feel vampiric. They may have been drawn to experiment with blood, blood drinking or bloodletting and found that it suited them.
Other traits include migraine headaches; various gastrointestinal sensitivities and problems, such as intolerance for milk-products, and food allergies/sensitivities; mood swings, depression, melancholia; an acute sense of separateness from those in "normal, mundane society"; above-average intelligence; possibly diagnosed with hyperactivity or attention-deficit disorder.
Having a number of these traits does not necessarily indicate that you are a vampire; it's just traits that we tend to have or suffer from. If you don't have a great number of the primary/secondary symptoms like bloodcraving, sensitivity to light, etc., then I wouldn't worry too much whether you're a vamp.
Do not take these traits and symptoms out of context. If you have a number of these, then, before you go off on your own assuming that you are a vampire, I highly recommend that you first go and get any symptoms you feel you have checked out with your doctor; you may find that they are quite treatable. Taken as a group, these traits and symptoms may indicate that you are a real vampire, especially if you have the bloodlust / blood cravings.
Sasha adds to what I've said: "And it cannot be overemphasized too much that such things like the migraines, sun-sensitivity, psychic abilities and stuff are mostly secondary symptoms (not like the bloodthirst or the beast inside). So that people are even more aware of the fact that having migraines and being depressive is not quite so much an indicator for being a vampire as is, for instance, blood craving."