As Anxiety is related to stress and obviously,it comes under psychological disorder which may be caused due to the deficiency of some important harmones and Neurotransmitters (chemical which transmits signals/impulses between neurons).Some of them are.. 

1. Serotonin
         Also known as 5-Hydroxy tryptamine(5-HT).It is a chemical substance (neurotransmitter) which is mainly responsible for giving pleasure.It is released during happiness,joy,pleasure etc.Decreased levels of 5-HT causes both Anxiety and Depression. Some medications like setraline, flouxatine raises serotonin levels and treats psychological disorders.

2. Endorphins
            These are Mood stabilisers by producing relaxation.These are endogenous neuropeptides / harmones released during excercise,pain,stress and produces relaxation by acting similar to opioids (morphine).Deficiency causes psychological disturbance and Anxiety.

3. Adrenaline/Noradrenaline
     The most important neurotransmitters commonly known as Flight/Fight harmones,which are Catecholamines. They relieves from stressful conditions and produces relaxation.
         Apart from these, others like GABA, Dopamine also released during Anxiety to relieve stress.Along with the above biological factors,some Genetic factors and Environmental factors also causes Anxiety.  

4. Genetic
        Due to familial history ,one may get affected with anxiety which may have been paased onto generations through their affected genes.

5. Medical
    Sometimes anxiety may be as a result of some other health issues like anxiety by hypertension,hyperthyroidism, Astma,allergy etc.,

6. Environmental
         A person’s lifestyle,unhealthy food habits,Trauma (Head injury),stress,neglecting by society can also causes anxiety.

How can be Diagnosed ?

        A person suffering from severe anxiety,can be examined by symptoms like increased Heart beats, Dry mouth,sweaty and numbness in palms and feet,sleep disturbances etc., it is best to consult a psychiatrist based on their psychological conditions.

Treatment

      
1. Anti-Anxiety drugs
        Azopirones like Buspirone, Ispapirone, Gepirones are used to treat anxiety.They have high affinity to 5-HT receptors and so bind to them and reduces anxiety.

2. Anti-depressants
    Selective serotonin reuptake inhibitors like Flouxetine, Sertraline, Flavoxamine and Nor-epinephrine reuptake inhibitors like Nortryptyline, Amoxepine, Reboxetine are mainly used drugs to treat Anxiety.

3. Benzodiazepines
          These are sedatives able to  relieve anxiety,but prescribed by physician very rarely only in severe cases,as they are addictive medications.

Natural remedies
      Apart from psychotherapy and medications,natural remedies works the best without any side effects.
   1. Regular exercise keeps out stress, relaxes and releives stress.
   2. Keep out of caffeine to stay away from anxiety.
   3. Herbal drinks like chamomile,valerian etc releives anxiety.   
                  

                Anxiety though, a part of life, extensive stress and anxiety leads to psychological complications.Healthy food habits and healthy lifestyle will keep you healthy and relaxed.Exercise regularly, meditate a few minutes to live peacefully. Asusual, smile is the best medicine as it increases serotonin levels. keep smiling.