Neck tension caused by stress or poor posture can result in a number of undesirable conditions, including headache, localized pain, and even dizziness. While finding and eliminating the underlying cause for your neck pain is the real key to preventing it from occurring again (by correcting your seated posture or removing stress from your life), there are a number of useful stopgap measures you can take to cure neck tension in the interim. Regular stretching throughout the day can help to keep your neck limber, alleviating dizziness in the process.
Perform cardinal neck stretches every couple of hours (or whenever you feel tension begin to build within your neck). Cardinal neck stretching is advocated by the Mayo Clinic--it involves stretching the neck to the front, the rear, and both sides in sequence. Begin by stretching your neck to the front. Sit upright with your shoulders relaxed and your spine straight. Initiate the stretch by bending forward at the neck until your chin comes into contact with your chest. You should feel tension in the back of your neck. Hold here for 10 to 20 seconds, then slowly relax. Next, reverse the stretch by bending your head as far backwards as possible (while keeping your body straight and your shoulders loose). Hold here for another 10 to 20 seconds. Follow this up by turning your head as far to the left as you are able, holding again for another 10 to 20 seconds, then repeating the motion to your right. Note that you should not be feeling any pain during these stretches--mild discomfort and tension is fine, but if you experience pain you are stretching too far and you should back off a bit.
Follow up your cardinal neck stretches with side to side neck stretching to further relax the neck, dissolving tension throughout the area. Begin by placing your right palm on the right side of your head, pressing your head gently to the side so that your left ear comes into contact with (or close to) your left shoulder. Maintain the pressure and hold the stretch for 10 to 20 seconds, being careful not to bounce or otherwise jostle your neck while in the stretched position. Relax slowly and reverse, using your left hand on the left side of your head to press your right ear into your right shoulder, holding for another 10 to 20 seconds. Make sure that you are actively bringing your head to your shoulder (thus stretching the neck), as opposed to cheating and lifting the shoulder up towards the head. Repeating these stretches several times throughout the day will help to remove the neck tension that is triggering your dizziness.