Very nice question…!
Insomnia is caused by several reasons as mentioned below;
(1) Ascendant lord placement & dignity
• Ascendant lord is debilitated
• Ascendant lord is placed in 12th house exception Taurus & Aquarius ascendants
• Ascendant lord is placed in 8th house exception Aries, Libra & Sagittarius Ascendants
• Ascendant lord is placed in 6th house exception Taurus, Libra, & Scorpio Ascendants
• Ascendant lord is with Malefics
(2) Moon is the karaka of mind – If moon is afflicted means…
• Moon is placed in either 6th or 8th or 12th house
• Moon is in conjunction with Ketu
• Moon is in conjunction with other malefics such as Rahu, Saturn & Mars
• Moon is placed in Scorpio or Capricorn sign
(3) 12th house is afflicted – placement of Rahu, &/or Moon, &/or Saturn, &/or Ketu, &/or Mars, &/or Sun, &/or Ascendant lord
(4) 8th house is afflicted – Placement of Ketu
(5) Moreover, highly creative people also does not sleep on time – they are sleep deprived – Placement of Rahu, / Moon / Venus in 5th house
(6) Person with debilitated Venus cannot sleep on time – person will have lots of dissatisfaction in the life
(7) Conjunction of Saturn + Ketu – person will have mysticism & occult pursuits so s/he always trying to solve the hidden mysteries of the world so their mind is highly occupied with absurd, aberrant thoughts & cannot get proper sleep.
(8) Ketu:
• Ketu’s placement in 1st house & 8th house
(9) Some special conjunctions…
• Moon + Saturn
• Moon + Ketu
• Moon + Rahu
• Moon + Sun
• Moon + Saturn + Ketu
• Venus + Mars + Rahu
• Saturn + Rahu + Mars
• Moon + Venus + Rahu