Maintain solid spinal alignment. Most people who are new to this will want to cheat the single-arm plank by creating cervical hyper-extension and tilting their heads up. This strains the neck and places excessive tension on the lumbar spine by causing the hips to sag.
Focus on keeping a tall and elongated neck throughout rather than tilting the head up or down.
It's estimated that 80% of the population will someday experience adrenal fatigue. When it comes to lifers, the percentage is probably higher. Jimmy Smith gives you 10 signs of adrenal fatigue, along with how to fix what ails ya.