Instabilities come in various types (vampiric, lycanthropic etc).
The trauma of Awakening gives a character instability (of the type the character was before the aspect merged with it).
Instability is reduced via Amelioration.
Building up specific types of instability produces the side effect of tainting the character with the vulnerabilities of that type of creature. This is measured in levels by comparing the amount of type specific instability to the same threshold values that release level, aura level etc use.
Vampiric Instability – Known Side Effects
Level 1: The sun seems bright today, need some sunglasses.
Level 2: Damn that sunlight is making my skin blister and peel.
Level 3: The Light, it Burns!! (one bashing damage per turn).
Level 4: Well, someone has achieved this – but so far so good…
Lycanthropic Instability – Known Side Effects
Level 1: you don’t know yet, you’re welcome to try it and see