That's true. But I was refering more to the fact that people with ADHD are CONSTANTLY overstimulated, more so than the average person, and people with ASD have a tendency to hyperfixate, more so than the average person. And so, people with either ADHD or ASD have a tendency to stress about a bunch of different things at once.
So, let's say the average person's mind is like a series of pipes:
There are liquid thoughts constantly flowing through the pipes, and there are some intercrossing sections where liquids mix and/or get filtered apart. Though the rate of flow in each pipe often increases and decreases, there is ALWAYS liquid flowing somewhere in the system, or else the entire system stops working.
There are pressure indicators on each section so that the brain knows how much pressure is in each section of pipe, and there are pressure valves so pressure in each section can be released if the pressure in that section gets too high. The pressure valves are connected to the sensors in the indicators, so that the valves can automatically be controlled, to prevent pressure buildup, and damage to the system. But, many of these valves can also be manually controlled via control wheels, so the brain's operator (the person) can direct and regulate flow to specific utilities and processes, as needed.
Now, for people with ADHD, the connections between the sensors and the valves are loose, causing malfunctions where the valves change direction unnecessarily. To make matters worse, the manual control wheels are a bit sticky, making it difficult for the operator to manually change the flow direction, even to fix the flow direction when the sensors malfunction.
For people with ASD, the connection between the sensors and the valves is fine, and the control wheels aren't sticky, but many valves are broken internally, so that flow is cannot be fully diverted between processes, so that some processes consistently receive overflow, while other processes are consistently unable to receive sufficient flow. In addition to that, many valve indicators are broken, making it difficult for the operator to determine how much flow each process SHOULD be getting, as well as how much flow each process IS getting.
For people with BOTH, all those issues are present. Because some of the the indicators are broken, the operator is unsure how much flow some processes SHOULD be getting, and is unable to recognize how much flow some processes ARE getting, so certain processes will get WAY too much flow, and others will get absolutely NO attention. Also, because of the faulty sensor connections, flow is randomly switched between processes, and it is difficult (or, in cases where the valve is broken, impossible) for the operator to manually redirect and regulate the valve direction. So, these flow issues will switch between processes at RANDOM.