Lemon Balm is a member of the mint family, it soothes the Nervous and Digestive Systems. It is a carminative herb, it helps with digestion and easing the abdominal muscles and relieving cramps. 
Lemon balm has a sweet, aromatic, lemony, cooling flavour and astringent taste. It is a great ally against stress and anxiety. 
"Lemon Balm contains the active compound "rosmarinic acid" - an enzyme which effectively increases GABA (gamma amino-butyric acid) in the brain. GABA is one of the inhibitory neurotransmitters, used by the brain to prevent over-excitement and attain balance. It is responsible for ensuring that we are not overly stressed and plays a role in sleep cycles. Increasing stimulation of GABA receptors will produce a sedative or calming effect and explains why Lemon Balm works well as an anti-anxiety herb."
"Lemon balm essential oil, or highly concentrated extracts have demonstrated benefits in relieving the symptoms of oral herpes infections or cold sores."
This herb help improving mental clarity, it is a diaphoretic with uplifting qualities.
​"For digestive relief, Lemon Balm is best consumed as a tea taken immediately after meals."

References

Gaia School of Healing and Earth Studies
Indigo-Herbs UK
Herbal Reality