A friend and I went in together on 125 broiler chicks that arrived last week. Only one was DOA. We each lost one that night. Then, of my remaining 19,all remained extremely active and healthy while she lost 2-3 per night for 5 nights before letting me know. She thought it was the chicks but no. I'm feeding mine Hiland Naturals while hers was on Purina flock raiser. Hers appeared to be having heart attacks. Now that she's switched feed back to her usual from a local place she hasn't lost any for a couple days...
Were you both depriving them of feed for eight hours overnight? It sounds like they died from either overfeeding or overheating.