Como eu posso Chan apontado no compêndio de Regras p.35

Imobilizado

"An immobilized creature can’t move out of the space it was in when it became immobilized. It otherwise functions normally unless it’s flying. Immobilized fl ying creatures that have the ability to hover can maintain their initial altitude. All other flying creatures subjected to this condition descend at a rate of 20 feet per round until they reach the ground, taking no falling damage."

No entanto, pode não ser a resposta que você está procurando.

Você deve dar mais atenção à primeira parte do efeito da magia.

Sigil de cobra sépia:

If the target fails its save, it is engulfed in a shimmering amber field of force[...].

While trapped in the amber field of force, the subject does not age, breathe, grow hungry, sleep, or regain spells. It is preserved in a state of suspended animation, unaware of its surroundings. It can be damaged by outside forces (and perhaps even killed), since the field provides no protection against physical injury. However, a dying subject does not lose hit points or become stable until the spell ends.

Basicamente você é como um inseto, preso dentro de um âmbar.