Ernst made a passing comment in one of his lessons how if one needs an excess amount of sleep, then their is a sort of medical/astrological issue. What might this be?
If we take sleep to be the period of time the body rejuvenates itself, then any situation or combination of situations during waking hours on outer and inner levels that cause stress load to be greater than the capacity to respond to the stress would create a necessity for longer time spent rejuvenating than what is typically required to keep the body functional. Greater stress periods have been described as malifics, dusthanas, negative avashthas, low dignity, etc. Stress load not dealt with builds over time and there are times where past stress and trauma emerge, if not recognized will cause a shutdown.
Venus as Karaka of rejuvenation, if poorly desposed in Rasi or D30 can implicate ones body takes longer to rejuvenate.
Consider the 6th house and it's influences.
Complexity with this question is that the SYMPTOM of "needing excess sleep" can have it's cause in the spiritual, mental, energetic, emotional or physical realm and typically the cause is too be found reverberating like waves in all these realms so start with the apparent and go towards the subtle. Ernst has addressed refining focus in teachings on identifying mental, energetic, emotional and physical weakness.
In the end I would focus on the astrological implications of stress and the bodies/minds ability/inability to process stress. Stress not singularly a psychological phenomena but corporeal, conceptual, mental, emotional, etc.