I encountered possibly the worst sort of windshear during my PPL training: 15kt straight headwind suddenly turned into virtually a tailwind, whilst we were coming in over the threshold, slow, and with idle power because it was a PFL.
Aircraft, Cessna 152, basically stopped mid-air, stall horn blaring, nose-drooped, and started to drop like a brick! Best I could do, with my hand being nowhere near the throttle, was just pull right back and yell "arghhhhhh" - luckily this (pulling back - not screaming!) did recover the nose and reduce the descent rate just before we hit the runway and I guess also the ground effect helped, so it ended up as a perfect touchdown, albeit at about 20kts. Instructor and I had a great laugh about it as we taxied off the runway - at the first intersection having used hardly any landing distance! He had thought we were going to die for sure... anyhow, we both learnt that it's best not to do PFLs during forecast windshear and gusty wind conditions... and that an extra 10kts is a useful precaution incase your headwind disappears at the critical moment...