It is normal to feel tired after lifting weights. Problems start to arise only when you begin to feel dizzy, nauseated or experience other unusual feelings shortly after an intense workout. It is common initially for the symptoms of an injury to feel like sickness in the stomach, but it is unlikely that lifting could injure the stomach itself. More likely is that you have injured the abdominals or another internal structure that is causing perceived feelings of sickness in the stomach.
Lifting weights can place a great deal of stress on the body. If you experience stomach illness or pains shortly after lifting weights, it is possible the injury occurred when you were performing a lift that placed significant stress on the abdominal muscles. Various techniques such as continuing to breathe rhythmically while lifting can help you reduce your odds of suffering a stomach injury from lifting, but you may be susceptible even with the right precautions.
It is possible for an injury to the abdominals to cause dizziness or even nausea for the lifter. You may notice the pain fluctuating depending on whether you are inhaling or exhaling. On the surface of your abdominal area you may notice a bulge of varying sizes. Coughing attacks may occur, and these often intensify the pain you are experiencing. Swelling may appear on the surface of the abdominals, and you are likely to find it difficult to lift at your normal workload.
In some cases, you may have suffered something such as a severe abdominal strain or even a tear of the abdominal muscles. Another common cause is the inguinal hernia, which occurs when part of the small intestine protrudes through a weak hole or tear in the abdominal muscles, according to the National Digestive Diseases Information Clearinghouse. Other causes may be possible, but it is less likely they are related directly to lifting weights -- it may be that the symptoms arose coincidentally while working out, or that lifting weights triggered the symptoms but is not the cause.
If your stomach pains persist or worsen over the course of a few hours, contact a doctor or visit a doctor's office. Your doctor may be able to diagnose your problem over the phone, but if you have a serious stomach injury, such as a severe inguinal hernia, immediate medical attention may be needed. If you experience any stomach pains in the middle of a workout, stop lifting, rest your body and take small sips of cool water.