Basically yea, but it's not so bad. It actually benefits you as an Atavistic Flame user to be using it quite frequently. The reason why I say that is due to the next technique:
(Ishi no Ikinobiru: Chūkū Hi) – Will to Survive: Hollow Flame
Type: Mode
Rank: A
Range: N/A
Chakra: N/A (-10 per turn)
Damage: N/A (+20)
Description: Will to Survive is an empowered state of spirit and soul, strengthening the user on multiple combat dimensions. The potency of the mode is divided between three different levels depending on the user’s mastery over their Atavistic Flame. Entering this form is comparatively complicated to Sage Mode even though the modes are similar in functionality. Atavistic Flame is recognized as humanity’s collective will to persevere; because of this it is actually optimal to activate the Will to Survive when the user is at their weakest, rather than at their strongest as is with Sage Mode. Upon activation Hollow Flame will take the user’s missing Health Points from their maximum and multiply that value by 4.5. This value represents the user’s total reserves for use of Atavistic Flame techniques and the mode’s sustainment. The mode is deactivated once the user has expended these reserves. The user becomes resistant to all sources of damage, reducing them by 20 points. The user becomes able to passively sense sources of life around their position with enhanced tracking, reflexes, and perception by x2. Their usage of Atavistic Flame techniques is enhanced further, strengthening them by an additional 20 damage. The user’s body will glow with a faint yellow aura and embers dancing off their skin; their sclera will shift toward a dim yellow. While active the user regenerates their missing Health Points at a rate of 30 per turn, applying to both physical and spiritual damage.
Note: Atavistic techniques used in this mode still inflict recoil damage if they do by default. Atavistic effective Chakra value is reduced from the total mode's resources while in use.
Note: While active the user does not suffer from Health Fatigue, spiritual or physical, at all.
Note: Initiates can use Will to Survive twice per battle. Masters and Grandmasters can make use of the mode three times per battle, but can only use their advanced forms twice.
Note: The activation of Will to Survive is not restricted by Combat Fatigue.
This is the actual mode, which uses your lower HP as a fuel for it. Talk to me about it and you'll see!