Overhealing

Healing another person is a dangerous act, particularly through magical means. Overhealing is a condition which is caused by being healed by potion. which has healing properties. Many healing substances work by enabling one's soul to absorb more Essence than it normal would. By increasing the intake of Essence, the person's natural healing process is sped up. However as the Sages of Highstar would say; "less means more, more means less."
Many scholars, priests and sages claim every life in this world of worlds have a limit of how much Essence they can take.

Symptoms

The signs when someone has been overhealed depends on the individual and how much Essence they have overloaded themselves with. Some relatively minor symptoms include: excessive energy, nausea, dizziness, shaking and sweating. Some people can also feel feverish as their souls try to adjust to the extra Essence.
The greater the overhealing the worse the symptoms can become. The minor symptoms already listed can escalate. In addition, those who have been overhealed can feel fatigue. In many case, there are those who have died from overhealing as well. Scholars would say the soul has burst from the excessive Essence, therefore not only killing the person but their soul too. Like filling up a watersack causing it to expand expand until it pops. Fortunately its the invisible soul which does this.

Everybody and everything has a limit of vitality. This is the way of nature.
There is no Essence, or Entropy; only Nature. Nature gives, nature takes. Nature hunts, nature survives. Nature hurts, nature heals.
The body is like a watersack, if you fill it up too much it spills. If you block the top as keep adding water into it, the sack will expand and eventually burst. Water is also heavy. Yes, it hydrates, but it can also drown. These healing concoctions work in the same way.
If you heal your body and soul too much, eventually they will cause you more problems. Headaches, tiredness, sickness, fever, and potentially death.

— A Sage explaining Overhealing