I have never had to declare minimum fuel in my whole career but this time was on the edge of doing so.
Usually numbers don't lie ... all you need is total fuel quantity, fuel flow and basic math knowledge ... and it shouldn't be such a hard decision making process for a mayday call!
Having said that ...
... since the level of readiness changes from pilot to pilot and varies with different scenarios ... your
Physiology,
Physical Status and
Motivation may have played some tricks on you ....
... so sensations, emotions and other non-normal feelings are to be consider as early warning of a worse situation to come!
When you have all the numbers ... a good rule of thumb is to keep your bravery for next landing ... and you'll never get in trouble!
You can always cancel a mayday call if you need to!