If an advancing moving (Moving in a particular direction) object (A) is accompanied by another differently moving object or device (B), unrelated to the motion of A, then the motion of 'B' will be affected by the motion of the advancing object (A). As 'B' (let 'B' is a clock) is located in 'A', 'B' will also be in motion in the direction of 'A' and its own motion will be disturbed. And as the speed of 'A' is faster than the speed of 'B', the speed of 'B' will keep decreasing. When the speed of 'A' attains the speed of light, or close to the speed of light, 'B' will become motionless or stationary. Here if 'B' is a living being, the action or activity within its body and mind will be affected by the motion of 'A' as mentioned earlier.
Not that 'Time' will slow down with the high speed of 'A'. 'Time' has no role here. 'Time' is actually nothing but the (measurable) distance between two actions or events. 'Time' is not a dimension either. It is not possible for a being (and its consciousness) to perceive higher dimensions than the dimension in which it resides.
'Time' is discussed in detail in the following research paper.
https://www.researchgate.net/publication/364339958_Unveiling_the_truth_of_'Time'_and_'Time_travel'_along_the_path_of_science