Is a conditional divorce considered valid, especially if it was merely a reaction to future whispers and delusions, and did not include an explicit pronouncement of divorce, with uncertainty regarding the exact wording or intention at the time?

What you mentioned are mere whispers (waswas) that have no consequence, and there is no basis for performing Istikhara regarding them. A sinner must conceal his sins and not expose himself. The suitor is considered a stranger to the fiancée until the marriage contract is concluded. We advise you to turn away from these whispers and beware of indulging in them. Seek help from Allah, sincerely resort to Him, and supplicate frequently to be rid of them.