Lose dynamic apnea personal record?

There are too many factors to effect your gains/losses. You may get in the pool after a month and feel great and set a new personal record. Or not.

What is your goal? bt. why you do train? you practice in a club or alone?

the worst you can do, is think about loses gains. You stress yourself, you can't relaxe and ka'tsching, you lose.
Always think about the pleasure, the silence and the joy in water. 50m or 100m, you do what you can and thats it. If you train too often also is negative. So always and everywhere train you relaxe skills and 3 weeks or 3 Month is not a big problem.

NEVER train alone!

For 95% of beginning freedivers their limitations are more mental than physical.

Mental gains certainly don't go away in three weeks but the body can detrain in that period.

Often the mental and physical go hand in hand, but there is a danger to more advanced divers and spearos who may not realize that while they are mentally able to do a certain dive, after enough time out of the water they may not have the conditioning....

See it with spearos, in the summer maybe a guy is diving hard 3 times a week, making gains in depth and overall comfort, mental barriers are falling and also the body is getting stronger and the physical limit is expanding. Then we have a stormy winter, same guy only dives once very couple weeks and has a hypoxic episode on what was a pretty normal dive a few months ago.