Yes you need salt, but it needs to be balanced with other electrolytes. I found this explanation on a medical website.
Electrolyte imbalances can cause a variety of symptoms, which depend on the specific electrolyte and the severity of the imbalance. Common symptoms include headaches, nausea, fatigue, muscle cramps, and weakness. More severe symptoms may include an irregular heartbeat, confusion, seizures, and coma. For example, hyponatremia, or low sodium levels, can lead to neurological symptoms such as headaches, confusion, and nausea. Hypernatremia, or high sodium levels, may cause symptoms like fast breathing, restlessness, and trouble sleeping.