It might be reasonable that Assensing could account for 'chills, dread, or other unnatural sensations'. But, then, the Rules say that one cannot default with that skill.
But, sensations, as in the five senses, whether they be natural or unnatural, may be environmental, as, for example, ozone, air pressure, or sound waves, from a Lightning Bolt. If active player Perception might be problematical, a threshold may be reached to cause the GM to request a dice roll for passive Perception.
And, Spells may have different thresholds, as further explained on p. 292 for resisting/overcoming Manipulation, and elsewhere for others. And, of course, it is up to the GM to evaluate and adjudicate the overall situation at hand.