Questions & Answers about כשהייתי לחוצה, הדופק שלי היה מהיר יותר מהרגיל.
כש־ means when. It is a very common shortened form of כאשר.
So:
- כש־ = when
- הייתי = I was
Together, כשהייתי means when I was.
In everyday Hebrew, attaching כש־ directly to the next word is very normal.
הייתי is the 1st person singular past form of להיות (to be).
So:
- הייתי = I was
- היה = he/it was
- הייתה = she/it was
In this sentence, הייתי refers to the speaker: when I was...