Which term would best describe a process occurring without immediate recognition?

The term "insidious" refers to a process that develops gradually and often without immediate recognition or noticeable symptoms. This is particularly relevant in medical contexts where certain diseases or conditions may progress in a subtle way, making it difficult for individuals to realize that something is wrong until it reaches a more advanced stage. For example, some chronic conditions may not present obvious signs early on, leading people to overlook the severity of the situation.

In contrast, "intact" generally denotes something that is unbroken or unchanged, thus not fitting the context of gradual or unnoticed processes. "Lethargic" describes a state of sluggishness or lack of energy, rather than a process of development. "Manifestation" refers to the expression or display of a symptom or characteristic, which implies a recognition or awareness of that condition, rather than the gradual onset implied by "insidious."