Nabooy/ rewNATION
I had this same issue when I got my iphone 6 on launch day. Basically now and then it would drop wifi and revert to 4G. If I when into wifi settings and toggled wifi off and on it would just say searching... And not display any networks and I live in an apartment with dozens of wifi routers nearby. The only fix was a hard reboot like you say with home and sleep/wake together.
It would happen about twice per day and after a few weeks I was at the Apple Store with a family member and asked if the could fit me in. I told them what had been happening and they swapped it out for a new one. I was really happy and got home and restored my iCloud back etc and low and behold it dropped wifi again about 2 hours after I got home! I assumed it was then software related so decided to just wait for a fix. Weirdly it's never happened again and I'm not sure if it was an iOS update or an app update whereby an app was causing the issue I really don't know but it's not happening for me anymore and it's been nearly two months without a reoccurrence. I'd like to say a new iphone would fix things but I'm not entirely sure that is the case as it happened on my new one hours after getting home and never done it since. It's worth noting I tried everything including setting up as a new device and resetting network settings at various stages before and after that. Nothing made a difference and I'm on the same router and location I was when I had the issues so the only change really has been software related.
Hope this helps although I didn't really give you an answer haha
The funny thing is, people had this issue while on the 8.0.2 but when they've upgraded to the latest, they no longer face this again. Another funny part is, it seems to work on all Wifi/routers except the one I use in my room. Isn't this weird? Is it because iOS is not fully supported with access point? Yes, it's not a router actually. I got my connection using my access point which is directly taking from the main router and while I've checked the main router which is in my brother's living room, it works like a charm with no issues, disconnections or whatever!
I just hope Apple are aware of this situation and are working on new updates to fix the whole Wifi issue otherwise it would be a letdown to many people especially for those who have switched from Android to iPhone such as me!