You have experienced "The Fear"

From what you have described I reckon you ought to give your next mushroom trip a miss.

You will potentially have the same experience.

A Bad Trip is generally caused by "anxiety" - you start to worry, your brain provides adrenaline in response to fear and this accelerates your heartbeat, and dilates your blood vessels.  So you get higher which leads to further anxiety and the flight or fight response your brain activates messes you.

The number one thing to remember when tripping is to chill out.  And make sure you feel calm and good before doing it.

Caffiene when you are tripping can be bad as it heightens anxiety, so avoid coffee and drinks like coke before and during.

Make sure you are in good company, in a good enironment and you feel safe and relaxed before you embark.

For best results I always reckon you should trip in daylight, morning, midday, early afternoon - tripping at night is less spectacular and tends to lead more easily to "the fear" in my experience, your mind is less likely to play tricks on you during the day when you can see clearly.

If you start feeling The Fear, distract yourself , do something else, get up and walk or whatever and try and slow down your breathing...

OH and the number one rule of all recreational substances "START SMALL" and be patient - wait for the effects before making a decision to have more, you can always take more later - or even save it for tomorrow when you will know how it all went.

You can always take more - but you can't take less...

I have seen many greedy people or people that think they can "handle" it go down the path of The Fear because the weren't patient.

The flashbacks you say you are having on weed are psychological most likely, you are thinking in some part of your mind that the same will happen again - so it does...

The Fear is a powerful enemy but can be overcome with a little common sense :-)

All of this is only my own humble opinion :-)