Complex sentence: Wills' mental instability is a source for medical speculation: epilepsy has been suggested as a possible cause of his perplexed mental state, and a variant of bipolar illness may account for his disjointed thinking and flowery, confused writings.
Split into simpler sentences: Wills' mental instability is a source for medical speculation. Epilepsy has been suggested as a possible cause of his perplexed mental state, and a variant of bipolar illness may account for his disjointed thinking and flowery, confused writings.