What does it mean if you have constant random flashbacks and visions of the future?

What is happening to you:
Reality is not a stable rigid place, it part of infinity and as such is subject to change. In an infinite existence that is subject to change anything can happen and it does. You are not what you think you are-you are more than you can possibly imagine because you exist in all these other realities and are connected to your other selves. You can feel them and your "past" self (which in truth is your present self). These "flash backs" are just memories and experiences from your other selves.

why do they happen?
There are an infinite number of reasons, here are a few:
1. Your third eye is activating or over active leading you to "see" beyond the ordinary realm of your reality into other realities using the eyes and bodies of your other selves.

2. A higher/more evolved other self is attempting to contact you or perhaps guide and teach you-unleashing your full potential and leading you move beyond your humanity into what people know as being a super-being or a god(ess).

3. You are experiencing the deja-vu phenomenon. The deja-vu phenomenon is when people feel that they have seen,heard, experienced a certain moment in "time" before even if this seems to defy logic because they have not experienced the events before. These deja-vu events can be anything-such as seeing a face or person you know you have seen before although you've never seen them before in your life.

What is the deja-vu effect?
Our existence is actually an infinity trap-in other words it is a closed existence that follows a specific energy patten which is not really "natural" and is not supposed to exist. This means that the whole of existence is infinite free energy (love energy) except the part of it we are trapped in. If you didn't understand this part don't worry.
The point is our existence/ our universe endlessly implodes and explodes in re-occurring cycles. When the universe comes to an end it implodes and restarts all over again. BUT-there are an infinite number of universes ending and beginning all at once and we feel the effects of this never ending cycle in the form of the deja-vu phenomenon. The reason we experience the feeling of deja-vu is because it really has happened before and is happening again in the infinite now (remember there is no past or future just an endless present)! Lots of times in fact. Everything has happened/is happening so many times that its like an endless echo is forming across time-space an echo of that which has already been and will be again.
You may be experiencing the echo of endlessness, the reason may be that you are evolving beyond being ordinary, your chakras are opening up letting in infinite energy into yourself.

What you should do:

Firstly don't panic or be afraid of your visions, lots of people have them,even me. Calm down and try doing some meditation, do some yoga to re-stabalize and open your chakras more. And remember one thing above all else, belief. Belief is the most powerful thing anyone possesses. it has the ability to change and shift reality/existence. If you get a bad vision of the future DO NOT be afraid of it, it is just a vision of something that may be not something that will be, believing in something that scares you lends it power-power enough to manifest into your reality from another reality. Remember you and no one else is in control of your own "future" and "destiny" as you understand them. If you believe in a positive future it will come to pass. If you really want something in life or existence believe with your heart and soul, believe to the bone and become your belief and you will get what you desire-and don't let anyone dupe you into thinking otherwise.