Lexus 400h left running overnight by accident

It may have run hot, since it was not moving little air would pass over the radiator which can cause it to run hotter than if it were going down the road. So check all the vital fluids, especially the coolant, make sure coolant isn't leaking from anything. If it appears to be running hotter than usual take it in and have the cooling system serviced. (new thermostat, change coolant, have hoses and water pump checked). No real harm should happen to a car in otherwise good condition from being left on for an extended period. I've worked on police cars that are often left to idle for hours at a time. Long term wear from that may include premature failure of the catalytic converter. I don't think you would have to worry about that unless yours was close to failing already. (You don't mention mileage or age of your car.) So take it in, have fluids serviced, and keep an eye on the temp gauge, if it does stay high report back here or have a mechanic look at it.

If everything looks good a high speed run on the freeway might be a good idea.

Hey guys, thank you for the reassurance and advise. I ran it on the highway and everything seems fine now. Toyota wanted to book me in to get it checked, but it seems to be fine now and i won't worry about them. My wife loves the car; its brilliant.

In my experience, the cooling fan failed and burned up making the smell. The overheating was caused by lack of air moving over the radiator.