There's a few things to consider biscuit mate. Your resting heart rate is not your heart rate when you are not exercising. Well it is, but that's not the way people measure it normally. The reason is, that various factors including whether or not you've eaten, taken any stimulants (sugar, coffee), your breathing, your emotions and psychology will influence your heart rate, and that's a good thing! The heart rate is controlled by the autonomic nervous system, which is in flux during the day, so it's supposed to change to changing demands. That's why there's a way to measure your resting heart rate to try to minimize these factors.
What you need to do is measure your heart rate when you are sitting or laying down and have been for some time. Let yourself relax for 10-15 minutes in calm surroundings and then take your heart rate. Do this maybe 3-4 days in a row and then do an average.
Just to clarify, 65-75 is not THAT high. Genetics play a factor as well and if you are in good shape, and you FEEL good and recovered, that's the most important thing. Don't get too attached to numbers. Mine is probably around 70-90 when I am with other people or out and about, but when I relax and calm down it sits around 50-65. Then again, working out will also have your heart rate higher for a few hours, and depending on the intensity, for over 24 hours. That goes with the whole overtraining thing.
1) Be sure to be rested and relaxed for a while before you take the readings
2) Do them over a few days
3) Be aware that various things can change your heart rate and that it's a good thing that the heart is plastic
4) Don't worry about it
If you insist, then try a little less high intensity, a little more LISS training and take time to relax during the day. Whatever makes YOU feel relaxed and calm, a book, relaxation techniques, thinking about nothing, drawing, so on. Do that for a few weeks to a month and see if it changes anything.
