ADHD and Almost 4 Year Old

My ds had his appointment with a Psychologist last week, and he says he has ADHD. He says he's VERY impulsive and VERY hyperactive. The attention is better. He spent the whole visit turning the lights on and off (about 100 times), opening and closing the door, running away down the hall, trying to get into everything in the room and he had huge tantrums when he was kept from doing these things. But he did much better when it was just the Psychologist and him doing testing. My ds is a handful, as the Psychologist mentioned as well. He needs constant supervision. He has a lock on his bedroom door when he sleeps, with little in his room. I just can't trust him with much. He is in no way aggressive, just impulsive and way too curious. He takes everything apart, breaks things, etc. He just cannot "let things be". I have two questions, so I'll start with one. How can I tell the difference between Sensory Seeking and ADHD? My ds is fine if he's getting enough input of some sort. He does much better after playing in water/sand and using his hands. He has to have something to manipulate in order to stay calm. But, if he is doing something with his hands, he is calm. We have an OT appointment in a month or so, but this has always bothered me. Also, the Psychologist thinks he should already be put on a low dose of meds. I was very surprised. He asked if this behavior is all day, and I said that it pretty much is. I can't trust him alone at any point. I also have trouble disciplining him, because he's SO fast and so out of control. I feel like typical discipline doesn't work with him. He is very athletic and I think he would love sports, but he can't focus enough to play them/enjoy them. Should I even consider starting meds already? I'm mostly worried about side effects.