it can be loads of horrible things or as simple as dehydration (which is serious but easily rectified), if you're feeling other wise okay in yourself Debs, though I'd still err on the side of caution and get a check over, blood pressure etc, have a look at how much water you're getting.
I never drink water and never have done since I left primary school, I drink loads of coffee though 😁
Yeah my blood pressure is always a bit on the low side, as is my pulse and resting heartbeat but my stress levels are low too.
I once got rushed to and admitted into hospital from work, ambulance the lot, as I was hyperventilating and when they did my blood pressure they went to get a different machine as it was so low they thought the machine was broken.