I am nearly 60 yrs old and have been on Singulair for some time. I have noticed mood changes but something even more alarming. My blood pressure usually runs a bit low but since going on Singulair, it has gone up. I have also had many instances of feeling faint and having to sit down and lower my head. I've had two incidents of E.R. treatment due to irregular heart beat, feeling faint, and elevated B.P. When I quit taking the medication for several days, my B.P. was again on the low side and I never felt faint. Although an irregular heart beat is an identified side effect, elevated B.P. and fainting are not. I would like to know if anyone else has experienced these symptoms, as the doctors have told me these are not side effects of the medication.