Aggressive or Assertive.........help please

Earlier on a shift this week I had a pt that was in for possible GI bleed. Consult with surgeon took place and decided to do colonoscopy the following morning. Got the MD orders and started bowel prep for following morning. Order stated to have Fleets phospasoda drank in 15 minutes and followed with24 oz of water. I knew that 15 minutes to have it all done by the patient was unrealistic. Anyhoo, over the next 45 minutes I checked back with the patient several times just to make sure that pt was drinking it. At this point he had only gotten down half of it when his son walks in. Now, all day long we had maintained a "pleasant relationship" the pt and myself. Son began asking me questions about what the plan was for his father so I told him what was to be done and what I was working on with the Dad at the time. I told him I was trying to get him to finish the drink. Son also reinforced the need for test purposes. Next thing I know the Dad says to the son. "I threw it up in my hand and it is nothing but salt". Of course this was news to me, he hadn't called to let me know and he had called me numerous times before to get up to BSC. Furthermore, there was no evidence of him throwing it up, linen dry, no towel at bed etc......I get the son a w/c b/c pt is wanting to go outside, fine with me, it was time for shift report. So almost finished with shift report, after time for me to be off, son calls nurse station to say the Dad had an accident in the w/c and was now on the BSC could someone come and change the linen. Charge nurse tells him she will have an aide there and the aide did go and get the linen changed promptly. Fast forward, pt coded at 0200 the following morning and passed. Same morning son comes back up to hospital and files a complaint and stated that I was "aggressive" with his father for all of the 10 minutes that we were in the room together.

The new DON comes to me the following day and asks me what was my take on the situation. I couldn't explain it to her b/c I have no clue what he was talking about. I have had my "mommy" hat on trying to get him to comply with the POC but didn't see how I was aggressive. I have never been an aggressive person in my life, I am the "wallflower", peacemaker, most non-competitive person period.

What is the real difference between aggressive and assertive. By definition, I would say assertive not aggressive and was not barking orders at the pt. This has really bugged me and I have relived the moments of the day and I am really perplexed by this and am having a hard time getting past it!!

Any advice, opinions, greatfully appreciated!! Sorry for the length.