WHY HAVE MY 2 DOGS STARTED FIGHTING?

Please help me!I have 2 rescue dogs approximately a year and a half in age each.Jack is a black labrador mix I rescued from the beach last november and Toby I found in some fields last february.They absolutely adored each other until last sunday when a scuffle broke out between them in the garden while they were playing.I didn't take much notice,just thought it was one of those things.Since then they have had little fights every afternoon until last evening,when they had 2 big fights and got really vicious and hurt each other.All of their fights have started when they have been playing until this morning when Jack when over to Toby twice just to say hello and Toby turned on him again.I don't understand what has happened.They adored each other and now Jack has become very weary of his little friend.Unfortunately I have MS and its not easy for me to get to them to help them when they do start fighting.Please can somebody help me!