Singulair and memory problems

My side effects have been mostly related to sleep. I have not slept well in several weeks. Waking up, horrible dreams, feeling like I have been yanked out of bed. When you do not sleep well, you will have memory problems, mood problems, muscle pains, and no energy. For the last few weeks, I have had to take naps every day. I have struggled with my college work as I am 49 and back in college. Can;t seem to remember what I have read or do any computations in my math class without help.
I have cut the dosage in half the past two days and have already noticed the difference. I am able to read and remember, sleeping better, no horrible dreams. Mood is definitely better. I need to keep taking this drug as it has been the only drug to help by nighttime asthma. I am now on 5 mg daily --which is a child's dose for ages 6-14.