Negative ions are actually good for you and for your health.
Negatively charged ions are located naturally by the sea, a waterfall or mountainous areas and are what give the air in those places that fresh feeling. They are also abundant during and after a thunderstorm.
Many man-made environments particularly those in which there are plastics or other materials which support or create static charge may suffer from ion (particularly negative ion) depletion which may be detrimental to the wellbeing and productivity of the people working and living in those environments. Positive ions are produced by computers, cell phones, televisions, air conditioners and power grids. They are also prevalent with pollutants in our environment like smog and smoke and are found in higher concentrations in the air in front of a storm or preceding the arrival of warm, dry winds. It has been observed, that coinciding with the higher concentrations of positive ions are more complaints of lassitude, depression, migraine, nausea, insomnia, irritability and respiratory disturbances.
Negative ions help neutralize the harmful effects of positive ions.
One study  found that negative ionisation is associated with a significant increase in performance as compared to subjects in a neutral environment. The study found that there was a highly significant increase in performance on tests for fine control, visual and auditory reaction times and rate control when the human subjects were exposed to negative ions as compared to those exposed to a natural environment or to an environment with more positive ions. In addition, it appeared that air ion levels affected the circadian rhythm of performance. Test subjects exposed to negative ions maintained a high level of performance throughout the afternoon and evening even when their circadian rhythm should have been falling. Subjects exposed to positive ions had an exaggerated decline in their circadian rhythms with their performance worsening rapidly and to a greater extent than the control subjects. Studies have concluded as well, that artificially increasing negative ion concentrations produces an improvement in cheerfulness and alertness while at the same time decreasing errors, lassitude and complaints of headache.
Other studies have linked increased exposure to negative ions to health benefits such as increased circulation, a boost in brain function, lessened feelings of depression, lessened effects from seasonal affective disorder (SAD) and balanced sleep hormones.
A study  done by Fusion found that with Fusion IONZ bracelets, which have a high negative ion output, test subjects reported an increase in energy levels and had a measureable performance increase in strength, balance, flexibility and muscle endurance.
Himalayan salt lamps release negatively charged ions and give off more negative ions the warmer they are (when they are lit for example). Salt lamps may aid in the treatment of headaches, sinus problems, allergies and hay fever, reduction of asthma attacks. They can also support the immune system because of the negative ions they release.
Fusion IONZ Bands contain a mixture of tourmaline, titanium and germanium in a silicon band. Germanium is thought to draw harmful positive ions away from the body. Health benefits of negative ions have been measured at 1000ng/cc. Fusion IONZ bands can emit up to 4000ng/cc which can be absorbed through your skin 24/7 if you always wear the band and can provide more health benefits.