Which condition arises within 20 minutes after a postretrobulbar block?

The condition that typically arises within 20 minutes after a postretrobulbar block is indeed more aligned with symptoms like near syncope and hypotension rather than unconsciousness. When a postretrobulbar block is performed, there can be a rapid onset of complications due to the injection of local anesthetic in proximity to the vascular and nerve structures.

Near syncope is characterized by a light-headed feeling or faintness and can occur due to a drop in blood pressure, which may also lead to hypotension. Hypotension can be a direct result of the local anesthetic affecting the sympathetic nervous system, leading to vasodilation and a decreased systemic vascular resistance, which in turn can cause a drop in blood pressure.

Unconsciousness, although certainly serious, is less likely to occur solely due to a postretrobulbar block within the initial 20 minutes. Complications such as seizures can occur but are not typical immediate responses after the block and often depend on other factors, including patient history and the specifics of the anesthetic used.

Thus, in evaluating the time frame and possible physiological responses to local anesthetic administration in this context, near syncope or hypotension is a more realistic immediate outcome than a state of unconsciousness.