Lost my ability to calculate

Idk how, but after my exam finished, somehow my game deteriorated.
I cannot calculate for long, all my moves are based on reflex.
I made no mistake in opening, and now it has also worsened.
In middlegame, I used to calculate long variations and now that ability has vanished.
I feel lost.
So, anyone knows how to get back to my primer self ?
I have a OTB tournament coming up in October.

heyyy...I guess we were sailing on the same boat...But I coped it up...and if u ask me how ,And i guess you have assumed the answer too, PRACTICE-PRACTICE...I used to read alot of books after the exams, calculating puzzles that included tactics and mates, Read books about strategical thinking, played long durations games online to help me thinking and avoided playing blitz and bullet...Well that's all I used to do and NO NEED TO WOORY IT HAPPENS BECAUSE WE HAVE BEEN STAYING OUT OF CHESS FOR ALMOST A WEEK...HOPE THIS WAS HELPFUL

Connect jumper cables to a car battery.

Connect the other end to one of your testicles. Connect the other end to your other testicle.

If done correctly, you will achieve shockingly fast results.

Stop playing blitz before an OTB tournament. 

try this exercise. Look at a position from a master game after both sides have castled. Take 5 minutes to come up with a pl for both sides. You will have to consider pawn structure, king weakness, and so on. Then play through the game and see how closely your analysis matched the play.

this gets you in the habit of long-range thinking, strategic analysis, etc. and gets you away from the cheapos and superficial tactics that you rely on in blitz.