are you using a little too much fertiliser? i had 2 plants drop on me, i cut down the fert to half therecomended dosage and after a week or so they where able to stand freely again, then i just put the fert quantities back up

its not a problem really if they do fall, they will just grow along and then up when they have enough strength, some people actually train there plants to grow horrizontally due to restricted height in there grow room amongst other reasons

my 2 that dropped i propped up with a bit of wire and made sure i had a fan blowing on them constantly, this improves stalk strength and also helps keep them with a nice fresh supply of co2 and gets rid of the 02 they putting out

id back the lights off slightly aswell maybe up to about6 inches - a foot to givethem a little break from the struggle, and maybe even consider giving them an 18/6 cycle as roots grow more during the dark period and the top during the day, mind you someone may come and totally rubish what ive said so give it a while for others to disagree or agree with me

h2h