Sun poisoning not only sticks you with the telltale, hot-to-the-touch, pink skin of sunburn; you'll also have a few more extreme (but still treatable) symptoms, such as dizziness, headaches, chills, or fever. Basically, if you come back from a day at the beach with a sunburn and flu-like symptoms, you can guess the culprit. Start treating sun poisoning at home by staying inside, drinking lots of water, using aloe or a gentle moisturizer, and even popping a few ibuprofen to ease the pain; sunburns and sun poisoning are both essentially major blisters on your skin. Sun poisoning usually doesn't reach the point where you need to up the ante and call your doctor — but if your case is so intense that you start to feel faint, head to a hospital.
You can prevent sun poisoning with the same methods you’d use to thwart a regular sunburn (sunscreen, sun hat, etc.) Be extra-vigilant in response to your area’s UV index, especially if you're fair-skinned. That, or really learn to love the shade.