Although it isn't obvious at first blush, and certainly not published, there is a big difference between Reiki practitioners, so-called "natural" healers and other energy healing methodologies. And that difference is fundamental. Put simply, Reiki healing is performed using energy coming from sources outside the practitioner, while most other such systems make use only of the healer's personal energy.
And so if you are so predispositioned and it is appropriate in your case, you can learn to heal AT SOME LEVEL but only by using your personal energy. Be warned: one of the biggest kept secrets is that most natural healers have lousy personal health; every time they perform a healing it depletes them and they suffer as a result.
Now, there are healing techniques that are an exception this issue, and that is the art of healing by transference. Unlike empathic healing, where the healer transfers the affliction to his own body which then heals the problem, transference moves the suffering through or in some way around his body into either some unfortunate animal, such as a chicken or pet, or as when I practice it, which is seldom, into a glass or bucket of water.
The final act needed to fix the cure is to kill the animal or return the water to the earth for purification. Since a certain amount of (poorly understood by most) ritual is involved with such a healing technology, I use it only for the most critical cases and usually only remotely to avoid causing more trauma or concern for those surrounding the case than already exists.
Like Reiki II, which I use in EVERY INSTANCE, immediate physical contact with the sick is not required, although getting a strong enough connection to perform remote empathic healings is sometimes difficult. (Empathic healing isn't fun; it hurts you as much as it hurt the subject.)
Reiki provides a certain degree of protection to the healer. But understand that is no means absolute, especially when used in combination with other techniques such as those just described.
As Takata said, "There is no wrong way to give Reiki." You cannot make a mistake, and there is certainly no magic to the hand positions; Takata taught that no matter where the Reiki entered the body it would eventually find its way to where it is needed most. (By the way, Takata taught only eight hand positions, all on the front side.)
But if you do not have the attunements, or if you decide to mix Reiki with other healing techniques, you aren't practicing Reiki and you are truly on your own.
Energy healing in general is not something to be trifled with. It is real, it is powerful. But it should first be used to heal yourself. And even after you are healed, a subject unto itself, only the pure of heart can use it in its most perfect and powerful form.
So in answer to your question, nope, you don't need the Reiki attunements. But who is going to teach you? Who will guide you until you understand enough so that you won't cause harm to yourself? A book written by some unknown, unproven, and unseen author?
My advice: don't try for a shortcut; even if you turn out to be capable of healing on your own, the energy you can give and manipulate is greatly limited compared to what you'll be able to deliver through Reiki.
Good luck! With love from the Corndodger
