Why Does My Heart Rate Go Up When Im Entering A Lucid Dream

Last night i woke up during the night so after going to the bathroom i decided to try FILD.After some time i felt like i was really close but my heart rate started going up like crazy.Any ideas on why that is or how i can overcome it.I dont remember if my heart rate went up everytime i tried FILD or WILD but last night i was really close and my heart rate stopped me from entering the dream.