How can one distinguish between the abundance of the remembrance of Allah and waswasah (whisperings/obsessive thoughts) and takhmat adh-dhikr (an excess/satiation of remembrance), and differentiate between striving diligently to ascertain the lawful and the unlawful and waswasah and extremism?

Whoever multiplies any kind of remembrance of Allah, he is among those who remember Allah frequently, and everything he undertakes to recall the meanings of the words of remembrance and repeat some of them is included therein. The best levels of remembrance are those performed with the tongue accompanied by contemplation of the heart. Striving to avoid what is forbidden is required, and part of piety is to avoid doubtful matters; for the Hadith of Nu'man ibn Bashir, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, said: "Indeed, the lawful is clear, and the unlawful is clear, and between them are doubtful matters that many people do not know. So whoever avoids the doubtful matters has cleared himself for his religion and his honor, and whoever falls into the doubtful matters falls into the unlawful..."

As for obsessive doubt (waswasah) and extremism, it is to abandon something based on a far-fetched doubt that is not supported by anything, such as refraining from marrying women from a large country for fear of consanguinity.