If someone insists on an immediate answer, the answer is always no.  Why is this?  It’s because when someone is trying to pressure me I become suspicious for good reason.  In my experience, when someone does not want me to have time to think a matter through it’s because saying “yes” is not in my best interest and may be harmful to me in the long run.  People who are simply asking and truly want the answer to be from my heart or what I feel comfortable with, do not mind giving me a chance to think about it before replying.  In fact, someone who is not trying to take advantage of me and really cares about me would never want me to agree to something that I would eventually regret.  Therefore, if someone has an interest in preserving our relationship for the future, they almost always insist on me thinking through the request carefully before agreeing to it.