In the case of sleep walking, this sleep phenomenon technically doesn't have the potential to disrupt or impact on the sleep cycle. I think it would be appropriate to comment on how sleep walking can only occur in the deepest stages of sleep (NREM stages three and four), as during REM, sleepwalking would be impossible due to the paralysis of the body during this stage. I wouldn't say that it impacts directly on the sleep cycle as such, as individuals would be extremely difficult to wake during a sleep walking episode (due to the deep nature of the sleep during NREM 3 & 4). After a sleep walking episode, a person may simply return to bed causing minimal disruption to the sleeping pattern.
With this question, you could also comment on the causal similarities between insomnia and sleep walking. That is, they can both be related to stress. A person can suffer from insomnia due to anxiety relating to important life events or relationships. Similarly, if a person is experiencing tension or stress in their lives, they are move susceptible to sleep walking.
Insomnia can significantly impact of the sleep cycle. Due to the poor quality of sleep, the amount of stage 4 NREM sleep and REM is reduced substantially.
Hopefully this helps.