It's definitely a weird phenomenon. You have an ejaculation, but there were fewer contractions...it didn't feel "complete." It's not that you didn't enjoy the sex, but you don't feel satisfied. You find yourself a couple of hours later with that heavy sensation and ache in your balls. Rather like you haven't shot a load in a month. A slight case of Blue Balls.
The build-up didn't hit its real peak, didn't really reach completion.
The average number of spasms hovers between 7 and 10, with the first usually being the strongest, ejecting the largest amount of semen, and decreasing from there to pretty much a twitch, or throb, and the cum oozing or dripping.
With the incomplete ejaculation, the tension hasn't been built to proper levels. If you sense you are about to cum, but you can't feel the gathering of fluid in the prostate, try to hold off. Cease any and all stimulation. Withdraw your cock, or, if you're jacking off, remove your hands. If need be squeeze off the path of escape at the very base of the shaft with your thumb and forefinger as tightly as you can.
Wait a few minutes until the sensation of immanent explosion passes,
then continue your activity.
Unsatisfactory ejaculations just don't cut it. You'll most likely find yourself stroking away a little bit later to complete the task of relieving the ache in your balls.