Fainting spells? Multiple occurences, when standing and stretching arms above head, and or yawning. W/ vertigo, fatigue, mental fuzziness, diarrhea

Improbable but... At your age a syndrome called "subclavian steal" is improbable; but, that or an autonomic dysfunction related to vagus nerve might be possible. Easy approach: see doctor, do the activity, look for pulse and BP changes. .